
Class Jltrh 



Book. 



3A^ 



Co|pghtN"_ 



COPyRlGHT DEPOSIT 



MATERIALS OF MACHINES. 



BY 

ALBERT W. SMITH, 

Professor of Mechanical Engi^ieering in 
Leland Stanford Junior University y California, 



FIRST EDITION. 
FIRST THOUSAND. 



J J J } J 



> }-. » ; K 3 . ' 



» ■ '3 J J 



j' ) JJ)J*3^ ')' 



NEW YORK: 

JOHN WILEY & SONS. 

London : CHAPMAN & HALL, Limited. 

1902. 






TWr LJBRARY OF] 
CONGRESS, 

■^^vo Copies Reck.ved 

AUG. 21 1902 

COPVRIQHT ENTRY 

riassOft^XXc. No. 
COFY B. 






Copyright, 1902, 

BY 

ALBERT W. SMITH. 




c ^ e 



ROBERT DRUMMOND, PRINTFR, NEW YORK 



PREFATORY NOTE. 



This book is a result of an effort to bring together 
concisely the information necessary to him who has to 
select materials for machine parts. 



Ill 



I 



CONTENTS, 



CHAPTER I. 

PAGE 

Outline of the Metallurgy of Iron and Steel i 

CHAPTER n. 
Testing. Stress-strain Diagrams 5^ 

CHAPTER m. 
Cast Iron ' 

CHAPTER IV. 
Wrought Iron and S ieel • 9 

CHAPTER V. 
Alloys ^ 

V 



MATERIALS OF MACHINES. 



CHAPTER I. 

OUTLINE OF THE METALLURGY OF IRON AND 

STEEL. 

Section i. Iron occurs in nature combined with 
many other substances. The world's supply of iron, 
however, is obtained almost exclusively from the 
oxides FCgOg and FCgO^. Carbonate ores, FeCOg, 
are reduced before smelting by roasting to FeO, and 
this FeO takes up more oxygen from the atmosphere, 
becoming Fe203. The formation of these oxides was 
accompanied by evolution of heat energy. This 
energy per unit weight of oxide was definite in 
amount and independent of the method or time of 
formation. To separate the oxide again into its con- 
stituents an exactly equivalent amount of energy must 
be supplied. In brief, the separation is accomplished 



2 MATERIALS OF MACHINES. 

as follows: Heat energy is supplied to the oxide 
whereby its temperature is raised. The bond which 
holds the iron and oxygen together, whatever its char- 
acter, is weakened. But this alone is insufficient in 
this case to cause separation. Therefore the heating 
is caused to occur in the presence of carbon or carbon 
monoxide. Either of these has greater affinity for 
oxygen at high temperature than the iron; hence, with 
the help of the heat, is able to pull away the oxygen 
from the iron oxide, forming COg, which, being 
gaseous, passes off, leaving the iron. The heat energy 
supplied to weaken the bond plus the energy expended 
by the carbon or carbon monoxide in pulling away the 
oxygen from the iron is exactly equal to the heat 
energy that was evolved by the original combination 
of the oxygen and iron into iron oxide. "^ The real 
process is much more complex because of circum- 
stances to be considered later. 

Sec. 2. Preliminary Consideration of Fuels. — In 
general a fuel is a substance which will unite chemically 
with oxygen with the evolution of heat. Nature fur- 
nishes many such substances; as, for example, silicon, 
sulphur, phosphorus, manganese. These are actually 
used for fuel in the metallurgy of steel, as will appear 
later. But the fuels used ordinarily depend for their 
value upon the presence of hydrogen or carbon. Fuel 

* By the law of Conservation of Energy. 



METALLURGY OF IRON AND STEEL. 3 

may be pure carbon (solid), pure hydrogen (gas), or a 
combination of the two, as petroleum (liquid). Fuel 
may therefore be a solid, a liquid, or a gas. 

Solid fuels are vegetable in their origin and consist 
chiefly of carbon, hydrogen, and oxygen. There is 
also a small amount of earthy matter present, which, 
being incombustible, remains after combustion and is 
called ask. When hydrogen and oxygen are present 
in fuel in just the right proportion to form water, the 
hydrogen is not available for combustion, as it is 
already in combination with the oxygen. But any 
excess of hydrogen is available as fuel. 

Sec. 3. Complete Combustion of a fuel element is 
its combination with that amount of oxygen which 
produces the most stable compound. Thus complete 
combustion of carbon produces CO2, carbon dioxide; 
and complete combustion of hydrogen produces H2O, 
water. 

Complete combustion of unit weight of any fuel 
element invariably produces a definite quantity of heat, 
which is called its calorific power. Since this is a 
quantity of heat it is expressed in units of heat quantity ; 
in this case British thermal units.* 

Calorific power of combustibles from experimental 
determinations : 

* A British thermal unit is the quantity of heat necessary to raise the 
temperature of one pound of water through one degree Fahrenheit at the 
temperature of maximum density. 



4 MATERIALS OF MACHINES. 

Coml)ustible. Calorific Power. 

Carbon. 14,500 British thermal units 

Hydrogen 62,000 ** '' << 

Carbonic oxide. ... 4,320 ** *' << 

Marsh-gas, CH/.. . 23,500 '' '' << 

If a combustible is burned in just sufficient air for 
complete combustion at atmospheric pressure, the heat 
evolved will raise the temperature of the gases, which 
pass off from the furnace where combustion occurs, 
through a certain definite range. The temperature 
thus attained is called the Calorific Intensity of the 
combustible, t 

Sec. 4. Determination of the calorific intensity of 
carbon. The combustion is represented thus: 

12 32 44 
C + O, := CO, 

The molecular weights are written above the symbols. 
For every 12 units of carbon 32 units of oxygen must 
be supplied, and for every one unit of carbon 32/12 
units of oxygen must be supplied. But the oxygen is 

^ Since one pound of marsh-gas is composed of 12 oz. of carbon and 4 
oz. of hydrogen, it would seem that its calorific power should be 12/16 
of 14,500 + 4/16 of 62,000 = 10,875 + 15^500 = 26,375 instead of 
23,500. The difference, 2,875, ^^ the energy used in separating the 
hydrogen from the carbon of the marsh-gas. 

f The temperature is raised through a certain range, and hence the 
final temperature attained will depend upon the temperature of the air 
which supplies oxygen for combustion. Hence this temperature must be 
added to the range due to heating to get the final temperature. 



METALLURGY OF IRON AND STEEL. 5 

supplied from the atmospheric air; and this is composed 
by weight of nitrogen, 0.77, oxygen, 0.23. Hence 
for every 23 parts of oxygen suppHed 100 parts of air 
must be supplied, and for every one part of oxygen 
100/23 parts of air must be supplied. Therefore, for 
the complete combustion of one pound of pure carbon 
the amount of air to be supplied equals 32/12 X 
100/23 = 1 1.6 lbs. The gases which pass off when 
the combustion of carbon is perfect are nitrogen and 
carbon dioxide. The nitrogen is inert as far as com- 
bustion is concerned. Its amount equals yy% of the 
air supplied, that is, 11.6 X 0.77 = 8.93 lbs. For 
every pound of carbon 44/12 = 3.66 lbs. of COg are 
produced. 

The heat evolved by the combustion of one pound 
of carbon is 14,500 B.T.U. This quantity of heat is 
available to raise the temperature of 8.93 lbs. of 
nitrogen and 3.66 lbs. of COg, and the resulting 
increase in temperature, /, is required. The specific 
heat of nitrogen equals 0.244, 3,nd of CO2 equals 
D.2164, and hence for every degree that 8.93 lbs. of 
nitrogen is heated there are used 8.93 X 0.244 
B.T.U. , and to heat it to the temperature /, 8.93 
X 0.244 X t B.T.U. are used. Similarly, to heat 
3.66 lbs. CO2 to /, 3.66 X 0.2164 X t B.T.U. are 
used. But the amount of heat that raised the temper- 
ature of both to / is 14,500 B.T.U. Therefore 
^(8.93 X 0.244 + 3-66 X 0.2164) =: 14,500; hence 



6 MATERIALS OF MACHINES. 

t = 4872° F., the increase in temperature. Assuming 
that the temperature of the air supporting combustion 
was 65° before combustion began, the calorific intensity- 
equals 4872° + 65° zzz 4937° F.^ 

Sec. 5. Determination of the calorific intensity of 
carbonic oxide. The combustion is represented thus: 

28 16 44 
CO + O = CO2 

Therefore, for every 28 parts of CO 16 parts of 
oxygen must be supplied, or for one part of CO 
16/28 parts of oxygen must be supplied, and for every 
part of oxygen 100/23 parts of air are required. 
Therefore, for every pound of CO 16/28 X 100/23 = 
2.48 lbs. of air are required. Of this air 0.77 = 
nitrogen = 1.9 lbs. Also the COg produced equals 
44/28 — 1.57 lbs. The weight of nitrogen heated 
therefore equals 1.9 lbs., and of CO2 equals 1.57 lbs. 
To raise the temperature of these gases 4320 B.T.U. 
are available. Hence 

4320 4320 ^ . ^ 

~(i. 9X0. 244)+(i. 57x0.2164)"" .803 ""^^ 

= the increase in temperature. Adding 65° as before 
gives the calorific intensity — 5345° F. In the case 
of carbon burned to CO2, 14,500 B.T.U. were avail- 

* Obviously the slight variations in temperature of the air supporting 
combustion have but little effect upon the calorific intensity. 



METALLURGY OF IRON AND STEEL, 7 

able to raise the temperature of 8.93 lbs. nitrogen and 
3.66 lbs. COg. The reason for the higher calorific 
intensity of CO is, therefore, that while the available 
heat is less, the weight of gases to be heated is less in 
greater degree. 

Sec. 6. Determination of the calorific intensity of 
hydrogen. The combustion is represented thus: 

2 16 18 

2H + O = HP 

For every part of hydrogen 8 parts of oxygen must be 
supplied. The corresponding amount of air = 100/23 
X 8 = 34.8. Hence the combustion of one lb. of 
hydrogen requires 34.8 lbs. of air. Of this 0.77 = 
nitrogen = 26.8 lbs. The water resulting from the 
combustion = 18/2 = 9 lbs. This water not only has 
its temperature raised, but it is converted into steam, 
and this steam is superheated. Supposing the conver- 
sion into steam to occur at atmospheric pressure, the 
heat required is 966 B.T.U. per pound of water. This 
heat has no effect upon the temperature, hence it may 
be subtracted from the calorific power of hydrogen, 
leaving the heat available for raising the temperature =: 

62,000 — (9 X 966) = 53.306. 

This heat is applied (first) to raise the temperature of 
the water from the temperature, t^, of the air-supply 



3 MATERIALS OF MACHINES. 

before combustion, to the temperature of vaporization, 
212° F. ; (second) to superheat the steam formed to 
the temperature /; (third) to raise the temperature of 
the nitrogen from t^ to t. The specific heat of water 
is i.o, of steam is 0.48, of nitrogen is 0.244. Hence 

(212 — /J9+ G'— 2i2)(9 X 0.48) 

+ (/ - /0(26.8 X 0.244) = 53,306. 

Whence, 

if /^ = 65° F., t = 4910° F. 

Hence, although the calorific power of hydrogen is far 
greater than that of carbon, its calorific intensity is 
about the same. The reasons for this are the greater 
relative weights of the substances heated, their greater 
capacity for heat, and the absorption of heat for the 
vaporization of water with no resulting change of tem- 
perature. 

The theoretical temperatures thus found are never 
attained, because (a) combustion is seldom complete; 
{b) an excess of air is always supplied; {c) the fuel is 
seldom entirely consumed; {d) there are always radia- 
tion losses ; {e) the moisture usually present in the fuel 
absorbs heat in being vaporized and heated; and (/) 
at high temperature the tendency of carbon and 
hydrogen to combine with oxygen is changed into a 
tendency to dissociate with absorption of heat and 
reduction of temperature. See Sec. 15. 



METALLURGY OF IRON AND STEEL, 

Sec. 7. Solid Fuels may be classified as: 
{a) Raw Fuels, such as coal and wood. 
{b) Artificial Fuels, such as coke and charcoal. 
Raw Fuels. Coal is often classified as follows 



Coal 



Lignite. 

Bituminous coal. 
Anthracite coal. 



Vegetable matter is really converted into coal by 
gradual change; hence each division of the classifica- 
tion covers a wide range and blends into the others. 
Description of coals is unnecessary here. 

The following table of percentage compositions 
shows the chemical changes which occur while woody 
fibre is changed to anthracite coal: 



Carbon. 



Wood 48. 5 

Peat 59.4 

Lignite 65.0 

Bituminous coal.. 78.0 
Anthracite coal. . 94.0 



During this change the percentage of available com- 
bustible increases, and the percentage of water to 
absorb heat decreases; hence the calorific intensity 
increases. 



H. & 0. in 

proportion to 

form water. 


H. avail- 
able for 
Combustion. 


50.9 


0.6 


39-0 


1.6 


33-0 


2.0 


19.0 


2.8 


4.0 


2.4 



lo MATERIALS OF MACHINES. 

Sec. 8. Wood. — According to Professor Thorpe,^ 
woody tissue when freed from soluble and other foreign 
matter has a percentage composition as follows: 
Carbon, 48.5; hydrogejl, 6.2; oxygen, 45.3. Since 
eight parts by weight of oxygen unite in combustion 
with one part of hydrogen, it follows that if the per- 
centage of hydrogen present were 45.3-^8=5.6-!-, 
the oxygen and hydrogen would be present in just the T 
right proportion to form water, and no hydrogen 
would be available for the evolution of heat. The 
amount of hydrogen really present is 6.2^; hence 
only the difference, 6.2 — 5.6 = 0.6,^ of hydrogen is 
available. This is practically negligible. Only 48^ 
of pure woody tissue is available for fuel. The calorific 
intensity is therefore low for this reason and also 
because the water resulting from the breaking up of the 
woody tissue, and that present as moisture, must be 
vaporized with absorption of heat unaccompanied by 
rise in temperature. Therefore wood cannot be used 
directly as a fuel for the production of very high tem- 
peratures. 

Sec. 9. Artificial Fuels. Coke. — Bituminous coal, 
as shown in the foregoing table, contains carbon, 
hydrogen, and oxygen. There is also a small amount 
of nitrogen present. 

If this coal be highly heated in a closed retort, it will 

* Coal : its History and Uses, pp. 164-5. Edited by Professor Thorpe, 
Published by Macmillan & Co. 



METALLURGY OF IRON AND STEEL, n 

not burn because of the exclusion of oxygen, but 
destructive distillation will take place. The products 
of this process may vary with the time occupied, the 
temperature, the quality of the coal, and other condi- 
tions, but in general are as follows: 

{a) Combinations of hydrogen and carbon in a very 
wide range of proportions, resulting in solid, liquid, 
and gaseous hydrocarbons. 

(^) Combination of hydrogen and nitrogen into 
ammonia. 

{c) Combinations of hydrogen, nitrogen, and carbon 
into aniline and many other compounds. 

{d) Combinations of carbon, hydrogen, and oxygen 
into phenol and other compounds. 

{e) Combinations of carbon and oxygen into carbon 
monoxide and carbon dioxide. 

(/) Pure hydrogen. 

{g) A nearly pure residue of carbon which is called 
coke. 

When sulphur is present, sulphur dioxide and other 
compounds of sulphur and the other elements present 
are produced. 

Sec. lo. Charcoal. — Wood may also be subjected 
to destructive distillation, the process being essentially 
the same as that just described. The carbon residue 
is called charcoal. 

The object of the processes for the production of 
coke and charcoal is to produce a concentrated fuel by 



12 MATERIALS OF MACHINES. 

removing all substances except the availabl*e fuel 
element carbon. Obviously this increases the tem- 
perature produced by combustion, i.e., the calorific 
intensity. 

Gaseous hydrocarbons, carbon monoxide, and hy- 
drogen are gas fuels which pass off, and hence, unless 
these are utilized, the process sacrifices a portion of the 
fuel in order to gain in calorific intensity. 

Sec. II. Gas Fuel has several advantages over solid 
fuel for many metallurgical processes. 

1 . Inferior solid fuel may be used for the generation 
of the gas fuel. 

2. The furnace for the production of the gas may be 
at a distance from the furnace where the gas is used, 
the transfer being made through pipes. Valuable 
space is thereby sometimes saved. 

3. Heat may be more easily applied uniformly over 
a given surface, or concentrated locally, with gas fuel 
than with solid fuel. 

4. The air which supports combustion can be much 
more completely mixed with the fuel, and therefore 
the excess of air over that necessary for complete com- 
bustion is reduced to a minimum, with a resulting gain 
in calorific intensity. 

5 . If the mixture of air and gas be properly regu- 
lated, there will be a complete absence of smoke and 
soot, and the latter will not be mixed with the material 
treated. 



METALLURGY OF IRON AND STEEL, 13 

Sec. 12. Production of Gas Fuel. —There are three 
processes for the production of gas fuel from solid fuel : 
Illuminating-gas process, water-gas process, and pro- 
ducer-gas process. 

Illuminating-gas Process, — Destructive distillation 
of coal containing a large percentage of volatile con- 
stituents. This process is similar to that for the pro- 
duction of coke, gas being the product and coke a 
by-product. The gas produced is illuminating-gas. 
Its composition is variable, but usually about as follows: 

H, 40 to 50^ by volume. 
CH,, 30 to 40^ - 
CO, 8 to 14^ '* 

There are usually also small amounts of CgH^, nitro- 
gen, oxygen, CO2, and vapor of water. 

Sec. 13. Water-gas Process. — Another method is 
to pass steam over incandescent carbon. The product 
is known as ^* water-gas.'* The reactions are as fol- 
lows: 

C + 2lip = CO, + 4H. 

CO2 + C = 2CO. 

CO + HP = CO, + 2H. 

These reactions probably go on simultaneously, and 
when the process is properly regulated the gas has 
about the following composition : 



14 MATERIALS OF MACHINES. 



CO,, 




2 to 


1 5^ by volume. 


CO, 




20 to 


40i " 


i i 


H, 




50 to 


65^ " 


it 


CH„ 




4 to 


H " 


a 


C,H. , 


etc. 


, to 


6fo " 


i ( 



When this gas is used for illumination it is passed 
through a second furnace, where it takes up vaporized 
hydrocarbons. 

Sec. 14. Producer-gas Process. — This process, the 
most important to the metallurgist, consists of burning 
coal with incomplete air-supply. 

Fig. I shows a form of gas-producer. It consists of 
a chamber, A, lined with fire-brick, and having suit- 
able grate at the bottom. Bituminous coal is intro- 
duced through a hopper, By so arranged that com- 
munication with the air need not be made when the 
solid fuel is put in. Air is admitted through the grate, 
and at D there is a steam-blower used to force combus- 
tion and to introduce steam. The chamber is con- 
nected to the gas-flue by the passage C The most 
rapid combustion occurs near the grate. The action is 
as follows: Air passes through the grate and combines 
with the incandescent carbon, forming CO^. This 
passes up and comes in contact with more incandescent 
carbon where the oxygen supply is small, and takes 
up more carbon and becomes CO, passing up into the 
chamber. In the upper part of the coal, where the 



METALLURGY OF IRON AND STEEL, 



15 



heat is less intense, the volatile constituents distil off; 
in fact, the action is the same as in the illuminating- 
gas retorts, with the production of hydrogen, hydro- 
carbons, carbon monoxide, etc. 

This, of course, leaves coke, which descends slowly, 




Fig. I. 

becoming incandescent, and uniting with the oxygen 
and CO2 to form CO. Also the steam from the blower 
passes through the grates with just the same result as 
in the manufacture of water-gas, viz., the production 
of hydrogen and carbon monoxide. Steam has an 
advantage over air, in that it carries no inert nitrogen 
to absorb heat, but it has the disadvantage of high 
capacity for absorbing heat, and if it be admitted in 



1 6 MATERIALS OF MACHINES, 

too large quantities it reduces the temperature in the 
furnace. 

An average of the resulting gases from this process 
is as follows: 

CO, 24.2^ by volume. 
H, 8.2^ ** 

CH4 2.2^ '' *' 

^C0„ 4.2^ - - 
N, 61.2^ '' '' 



Combustible - 



Incombustible ^ 



Sec. 15. Therefore 34.6^ of this gas is combustible, 
while 65.4^ is incombustible, and hence it must be 
a fuel of low calorific intensity. It would seem, there- 
fore, that ** producer gas" could not be used for 
producing high temperatures. It becomes available 
for this purpose, however, through the Siemens 
Regenerative Furnace, the invention of Messrs. Fred- 
erick and C. W. Siemens. The gas, instead of being 
admitted to the furnace directly, passes through a 
chamber, ^ (Fig. 2), filled with *' chequer work," i.e., 
full of small intricate passages, surrounded by refrac- 
tory material suitable for absorption of heat. The air 
also passes through a similar chamber. Ay and meets 
the gas at C, the entrance to the hearth D, where the 
metal is treated. The air is admitted above the gas, 
so that, because of its greater specific gravity, it shall 
mix more completely with the gas. Combustion occurs 
at Cy and the products of the combustion, heated to a 



METALLURGY OF IRON AND STEEL 



I? 



temperature corresponding to the calorific intensity of 
the fuel, pass over the hearth and through the cham- 
bers A^ and B^ to the stack. In passing they heat up 
these chambers to their own temperature, if the process 
is sufficiently long continued. Then the connections 
are changed so that the gas comes in through B^y and 




Fig. 2. 



the air-supply through A^ , and A and B are connected 
with the stack. The gas and air passing through the 
heated chambers have their temperature raised before 
combustion takes place; then the temperature is still 
further raised by the combustion, so that the products 
of combustion now pass to the stack through A and B 
until the temperature of these chambers is raised to this 
higher temperature. Then the connections are again 
reversed and the entering gas and air are heated to this 
higher temperature before combustion, and so on. It 



1 8 MATERIALS OF MACHINES. 

would seem that an indefinitely high temperature could 
be produced in this way, but a limit is set at about 
4000° F. The reason is as follows: Carbon is slowly 
oxidized at atmospheric temperatures. As the tem- 
perature is raised the tendency for carbon and oxygen 
to combine becomes stronger. The strength of this 
tendency increases with the temperature, but reaches 
a maximum, and then decreases with increasing tem- 
perature. Finally the tendency becomes zero, and 
further increase in temperature results in the dissocia- 
tion of CO or CO2 , with corresponding absorption of 
heat. The temperature varies in different parts of a 
furnace using solid or gas fuel, and when the average 
temperature is high (say 2500° or 3000° F.), probably 
both combination and dissociation of carbon and 
oxygen, or of carbonic oxide and oxygen, occur simul- 
taneously; the combination evolving heat and the dis- 
sociation absorbing heat. If the evolution of heat ex- 
ceed the absorption, the average temperature will rise ; 
but if the absorption exceed the evolution, the average 
temperature will fall. Suppose that the conditions are 
such in a furnace that combination exceeds dissocia- 
tion, it follows that the temperature will rise; but in 
rising it approaches that temperature at which com- 
bination and dissociation are equal. At this tempera- 
ture there is no increase of heat, and therefore no 
tendency to raise the temperature; hence it is the 
highest temperature that can be attained. The steam 



METALLURGY OF IRON AND STEEL, 19 

which results from the combustion of hydrogen may be 
broken up again into hydrogen and oxygen if the tem- 
perature be sufficiently raised. 

From this it follows that in a Siemens regenerative 
furnace using fuel composed of carbon and hydrogen, 
the temperature that can be produced is limited. 
Experience shows that this limit, under ordinary con- 
ditions, is probably about 4000° F. 

Sec. 16. Refractory Materials. — Furnaces and 
receptacles for metallurgical work require to be lined 
with material that is capable of withstanding high tem- 
peratures, i.e., refractory material. 

Fire-clay is a hydrated silicate of alumina with 
excess of silica and with small and varying percentages 
of lime, magnesia, and oxide of iron. Because of the 
presence of water of hydration fire-clay has the quality 
of mixing mechanically with water and becoming plas- 
tic. It may then be moulded into any required form, 
the mechanically mixed water may be removed by 
drying and the water of hydration may be removed by 
** burning" or calcining. A hard, strong, and very 
refractory material — anhydrous aluminum silicate — 
results from this process. The tendency to shrinkage, 
distortion, and cracking during burning is partially 
neutralized by mixing coke-dust, graphite, or silica 
sand with the plastic clay. 

Ganister is fire-clay with very great excess of silica. 
It is changed in volume only slightly by burning, and 



20 MATERIALS OF MACHINES, 

hence it may be formed while plastic into the furnace 
itself and burned in place. 

Fire-clay is acidy and when a basic furnace-lining is 
required Dolomite — Magnesian limestone — is used. 
It consists of carbonates of magnesia and lime from 
which the carbon dioxide is driven off by calcining. 
The resulting mixture of magnesia and lime has little 
coherence and hence it is coarsely ground and mixed 
with tar into a plastic material, which is formed into 
the furnace-lining. Heating then cokes the tar and it 
becomes a cement for the magnesia and lime. 

Sec. 17. Sources of Iron. — Full consideration of the 
ores of iron is beyond the scope of this work.^ 

Iron ores may be classified as follows: 

1. Magnetic oxide, or Magnetite, Fe30^. 

2. Ferric oxide, or Red Haematite, Fe^O^. 

3. Hydrated ferric oxide, or Brown Haematite, 
Limonite, Bog ores, etc. 

4. Ferrous carbonate or Spathic ore, FeCOg. 
These ores always carry other substances, and the 

proportions vary between wide limits. The following 
table t gives some idea of these proportions. 

Magnetic oxide, Fe304 , may be regarded as a com- 
pound of ferrous oxide, FeO, and ferric oxide, Fe^Og. 

* Ore Deposits of the United States, J. F. Kemp ; Scientific Publish- 
ing Company. Iron (The Metallurgy of), T. Turner; J. B. Lippincott 
Company. 

•j- Condensed from a table given by T. Turner in Iron (The Metal- 
lurgy of). 



METALLURGY OF IRON AND STEEL. 



21 



Ferric oxide (Fe203) 

Ferrous oxide (FeO) 

Manganous oxide (MnO) 

Carbon dioxide (COg) 

Silica (Si02) 

Alumina (AlgOg) 

Lime (CaO) , 

Magnesia (MgO) , 

Phosphoric anhydride (PgOg) 
Water 



Magne- 
tite, 
Swedish. 



65 
25 



10 



0.03 



Red 
Haema- 
tite, Cum- 
berland. 



90 



0.04 



Brown 
Haematite, 
Northamp- 
ton. 



65 
0.5 



13 

3 



1.3 
14 



Carbonate, 
Stafford- 
shire Clay- 
Ironstone. 



0.5 
47 

2 

30 
10 

5 

2 

2 
0.04 

I 



The ore may also contain sulphur and arsenic. 
These, with the carbon dioxide and water, may be 
removed as vapoi or gas, at comparatively low tem- 
peratures, by the process of calcining or roasting. 

Sec. 18. For Calcining or Roasting the ore is piled 
in heaps out of doors, or charged into kilns, with fuel 
in proper amount mixed with it. The fuel is ignited, 
the mass is slowly heated up. Water is driven off as 
steam. If the ore is carbonate, FeCOg, the CO2 is 
driven off, and the resulting FeO is changed to FcgOg 
by combination with oxygen of the air. If any iron 
pyrites, FeSg , is present the sulphur is oxidized, pass- 
ing off as SO2, while the iron is also oxidized, remain- 
ing as Fe203. Arsenic is oxidized and vaporized if 
present. By the process of roasting the structure of 
the ore is made more open, and hence better fitted for 
smelting. 

When roasting is carried on in kilns it is often a 



2 2 MATERIALS OF MACHINES. 

continuous process. The kiln is like a foundry cupola, 
much enlarged in diameter. The ore and fuel are 
charged in at the top, and the roasted ore is withdrawn 
from openings at the bottom. 

The process is now usually omitted for oxide ores, 
the roasting being accomplished in the top of the blast- 
furnace stack. 

Sec. 19. The early methods for the production of 
iron were direct methods^ i.e., the product was zvr ought 
iron, which had not passed through the intermediate 
state of cast iron. 

Chemically these methods are as follows: Rich ore, 
Fe203, or Fe30^, is charged with charcoal into a 
rectangular hearth, and air-blast is supplied. The 
coal is ignited and the oxygen of the air combines with 
the carbon of the fuel to form CO2, which passing on 
over more incandescent carbon is reduced to CO, 
which comes in contact with the Fe203, when the fol- 
lowing reactions take place: 

3FeA+CO =2Fe30,+ C02 
2Fe30, + 2CO = 6FeO + 2CO2 
6FeO + 6C0 = sFe^ + eCO^. 

MetalHc iron and COg are therefore produced. But 
the ore also contains some siHca, alumina, etc., which 
are very infusible, and which must be rendered fluid for 
removal from the iron. It happens that silica and 
alumina unite with FeO to form a double alumino- 



I 



METALLURGY OF IRON AND STEEL 23 

ferrous silicate or slag, which is fusible at a low tem- 
perature. Some of the FeO which is produced during 
the process (see above reactions) acts as a ^'Jltcx,'^ 
i.e., renders the earthy matter fluid, separating it as 
fluid slag, which may be partly drawn off, while the 
iron remains in the hearth a spongy mass filled with 
molten slag. The mass is heated to a welding tem- 
perature and taken to a hammer or squeezer, where 
the slag is removed by impact or pressure, and the 
mass is welded into a bloom. 

The details of the carrying out of this process vary. 
It requires rich ore, charcoal for fuel, and the waste of 
iron in the slag is very great. It is a very expensive 
process, and is not available for the production of large 
quantities of iron. 

Sec. 20. Nearly all the iron used to-day is reduced 
from ore in the Blast-furnace. Fig. 3 shows a vertical 
section of a blast-furnace. The height varies from 40 
to 100 feet, and the diameter at iJ/ varies from 12 to 
25 feet. The inside form varies with the kind of ore 
and fuel used, and with the pressure and quantity of 
air of the blast. 

A blowing engine supplies air, at a pressure of from 
5 to 15 pounds per square inch, to the large pipe, P, 
which surrounds the stack. At intervals of the cir- 
cumference of this pipe smaller pipes convey the air to 
the tuyeres, T, which deliver it into the furnace. The 
oxygen of the air combines with carbon of the fuel and 



24 



MATERIALS OF MACHINES. 




METALLURGY OF IRON AND STEEL, 25 

forms carbon dioxide, which is almost immediately 
reduced, in the presence of carbon with restricted 
oxygen supply, to carbon monoxide. There is a con- 
stantly ascending current of carbon monoxide and 
nitrogen through the constantly descending solid 
materials. 

The ** bell,'' B^ prevents the escape of gas from the 
top of the stack, and insures its delivery into the 
pipe, G. Solid materials to be introduced into the 
furnace are placed in the annular space above B^ and 
the latter, which is controlled by power, is lowered 
periodically and the charge drops into the furnace. 

The function of the blast-furnace is to change iron 
ore into pig iron. 

Pig Iron is iron carrying from 3 to lofo of carbon, 
silicon, manganese, sulphur, and phosphorus, either 
chemically combined or mechanically mixed. 

The blast-furnace, therefore, provides for — 

{a) The removal of volatile constituents of the ore. 

(J?) The reduction of the iron oxide of the ore. 

{c) The removal of the solid earthy constituents of 
the charge. 

It also provides carbon, silicon, manganese, sulphur, 
and phosphorus under proper conditions for absorption 
by the iron. 

In order that the earthy solids of the ore shall com- 
bine with the flux into a readily fusible slag, silica, 
alumina, and lime must be present. If the ore carries 



26 MATERIALS OF MACHINES. 

silica and alumina, it is only necessary to introduce 
lime, and the flux is limestone. If an ore contains 
silica only, alumina may be introduced with lime; or, 
siliceous and aluminous ores may be mixed and fluxed 
with limestone. 

Sec. 21. Chemical Changes in the Blast-furnace.* 
— Ore, coke, and limestone are charged into the top 
of the stack and descend slowly to the crucible, O, at 
the bottom. The ore is first roasted, t and then, when 
the temperature has reached about 400° F. the reduc- 
tion of iron oxide by carbon monoxide begins slowly 
and continues at an increasing rate till the temperature 
reaches about 1 100° F., when the reduction is probably 
nearly complete. The ore has now become a sponge 
of metallic iron mixed with silica, alumina, etc. But 
at this latter temperature the flux, which is limestone, 
CaCOg, begins to give off COg, and the lime, CaO, 
thus produced comes in contact with the silica and 
alumina of the reduced ore, and they descend together 
till a temperature is reached at which they combine to 
form a fusible slag, which melts and leaves the iron 
sponge. 

Introduction of Carbon* — In the meantime a deposi- 
tion of carbon upon the iron sponge has been going 
on. This may be explained as follows: When carbon 

*Iron (The Metallurgy of), by T, Turner; J. B. Lippincott Com- 
pany. 
I See Sec, 18, 



METALLURGY OF IRON AND STEEL, 27 

monoxide passes over metallic iron at a temperature of 
about 750^ F., the carbon monoxide is decomposed, 
solid carbon is deposited, and carbon dioxide and 
ferrous oxide are formed. This is what occurs in the 
blast-furnace when the temperature of about 750° F. is 
reached by the metallic iron sponge. Then, as the 
temperature rises, ferrous oxide is reduced again by 
carbon monoxide, or by solid carbon, the carbon 
dioxide passes on upward with the gas-current, and 
the iron sponge remains impregnated with carbon. 
As this passes on down with increasing temperature, 
iron carbide is formed, which is fusible at a much lower 
temperature than pure iron; a temperature which is 
reached below M in the blast-furnace. Therefore the 
descending iron carbide is raised to its fusion tempera- 
ture and melts and falls into the crucible O. 

Introduction of Silicon. — At very high temperatures, 
in the lower part of the furnace, where carbon and 
silica and metallic iron are in contact, a portion of the 
silica is reduced, and the resulting silicon is taken up 
by the iron. This change is favored by {a) high tem- 
perature, {b) excess of silica in the charge, and (c) 
deficiency of lime in the slag. Usually not more than 
5^ of the silica of the charge is reduced. 

Introduction of Manganese. — The manganous oxide 
of the ore is not reduced by carbon monoxide, but is 
in part reduced by carbon at high temperatures, and 
the resulting manganese combines with the iron. The 



28 MATERIALS OF MACHINES. 

unreduced manganous oxide passes into the slag. 
Certain ores, like New Jersey Franklinite, contain very 
large proportions of manganous oxide, and the product 
of their smelting is Spiegel-Eisen, containing from 5 
to 25^ manganese. 

Introduction of Sulphur* — Only a small part of the 
sulphur in the charge, which is chiefly in the coke as 
iron sulphide, FeS, appears in the pig iron, the rest 
passing into the slag as calcium sulphide. The 
amount of sulphur that the iron can take up depends 
upon the capacity of the iron itself for sulphur, and 
also upon the amounts of silicon and manganese 
present. Both of these substances seem to crowd out 
sulphur to a certain extent. High furnace temperature 
tends to reduce the amount of sulphur in the pig iron. 
Also basic slag, i.e., slag with excess of lime, com- 
bines readily with sulphur, thereby reducing the 
amount absorbed by the iron. 

Introduction of Phosphorus. — The phosphorus of 
the charge is usually in the ore in the form of calcium 
phosphate. This is not changed by carbon monoxide. 
But when the part of the furnace is reached where the 
slag is formed, the calcium phosphate is reduced in the 
presence of solid carbon. The lime goes to the slag; 
the phosphoric anhydride is broken up with formation 
of carbon monoxide and iron phosphide. Practically 
all of the phosphorus of the charge appears in the pig 
iron. 



METALLURGY OF IRON AND STEEL. 29 

Descent of Coke. — Coke is the fuel almost uni- 
versally used in ** hot-blast" furnaces. As the coke 
descends it is dried and raised in temperature. It 
meets carbon dioxide, which may come from the 
reduction of iron oxide, or from the roasting of car- 
bonate ore, or from the roasting of limestone. The 
carbon dioxide is reduced to carbon monoxide with 
absorption of heat. The resulting carbon monoxide 
may take part again in reduction, or, if it be near 
the top of the stack, may pass off unchanged with 
the gas-current. The coke may also supply part of 
the carbon for formation of carburetted iron, and it also 
helps in the reduction of silica and phosphoric anhy- 
dride. When it reaches the vicinity of the tuyeres it 
burns to CO and evolves the heat necessary for the 
operation of the furnace. All of the carbon of the 
coke appears either in the pig iron or in the gases 
issuing from the top of the stack. 

Sec. 22. The combination of iron, carbon, silicon, 
manganese, sulphur, and phosphorus is fusible at a 
temperature which is reached a little below M in the 
blast-furnace. Hence fusion occurs and the melted 
substance falls into the crucible, O, together with the 
fluid slag. The iron and slag separate because of their 
difference in specific gravity, the slag floating on the 
top. When a sufficient amount has accumulated, the 
slag is tapped out through the ** cinder-notch," 
allowed to cool, and transferred to the ** cinder 



30 MATERIALS OF MACHINES. 

dump. ' ' The iron is tapped out through a hole low 
down in the crucible and allowed to run out through 
properly formed sand channels, where it cools as pig 
iron. 

Sec. 23. From what precedes, it follows that a con- 
tinuous current of gas flows from the top of the blast- 
furnace stack. The chief constituents of this are 
nitrogen, carbon dioxide, and carbon monoxide. 
When the furnace is properly regulated, the carbon 
monoxide equals about 25^ of the issuing gas. It is 
therefore a gas fuel. A portion of this is conducted to 
the boiler furnaces to make steam to run the blowing 
engines and other auxiliary machinery. The rest is 
used for heating the blast. 

Sec. 24. Hot Blast. — In early blast-furnaces the 
blast entered the furnace nearly at the temperature of 
the outside air. Cold blast is still used in furnaces for 
the smelting of some special grades of iron. 

Heating the blast on its way from the blowing 
engine to the tuyeres results in: 

(a) Economy of Fuel, because the blast is heated 
by the waste gas fuel from the top of the blast-furnace 
stack, and less fuel needs to be burned in the furnace 
to maintain a given temperature. 

{b) Increased Capacity, because, since less coke is 
charged, ore and flux may take its place. 

{c) Grayer Pig Iron. — The furnace temperature is 
higher with hot blast, and this favors the reduction of 



METALLURGY OF IRON AND STEEL. 3^ 

silica, and the presence of silicon in the iron causes a 
large part of the carbon to crystallize out as graphite, 
i.e., it renders the iron gray. 

The first method of heating the blast was to pass it 
through cast-iron pipes, which were enclosed in a fur- 
nace and maintained at the highest temperature that is 
safe for the material of the pipes. This temperature, 
however, is only about 900"" F. In order that a higher 
blast temperature may be reached, special hot-blast 
stoves have been designed. The Cowper type is 
shown in Fig. 3. It consists of a cylindrical shell of 
iron plates lined with fire-brick. C is a combustion- 
chamber, and Z^ is a chamber filled with ** chequer 
work. ' ' The gas fuel from the top of the stack passes 
through the pipe (9, the dust-separator H, and into the 
combustion-chamber at J. Here it meets air which 
enters at A, and combustion takes place. The heated 
products of combustion pass down through D and on 
through E to the chimney. This process is continued 
till all the combustion-chamber and the chequer work 
are raised to the temperature of combustion. In the 
meantime the air from the blowing engine enters the 
other stove (which has been previously heated) at K, 
passes up through the chequer-work chamber, and 
down through the combustion-chamber. The air 
gains heat from the chequer work and is thereby raised 
to a temperature somewhere between 1000° and 
1500° F. It then passes through L and P to the 



32 MATERIALS OF MACHINES. 

tuyeres, Z", where it enters the furnace. When this 
stove is cooled down so that the blast is insufficiently- 
heated, properly arranged valves are changed, and the 
gas burns in the stove at the left, while the blast enters 
through the stove at the right. 

Since the action of the blast-furnace is continuous, 
there must be at least three stoves, so that any 
one may be put out of service for cleaning or re- 
pairs. 

Sec. 25. There are some blast-furnaces that use 
charcoal exclusively as fuel, with cold blast. The 
product is white iron. Because of the lower tempera- 
ture in the furnace less silica is reduced, and less 
silicon absorbed by the iron. Because of the small 
amount of silicon the carbon combines with the iron, 
instead of separating as graphite, and the iron fracture 
is white. This iron is used for chilled car-wheels, 
malleable cast iron, etc. 

Sec. 26. Pig Iron from the blast-furnace goes either 
{a) to the foundry to be converted into castings, or {b) 
to the puddling mill to be converted into wrought 
iron, or {c) to the Bessemer mill to be converted into 
Bessemer steel, or {d) to the open-hearth furnace to 
be converted into open-hearth steel. 

Sec. 27. In the Foundry pig iron is melted, with 
very little chemical change, and poured into sand 
moulds, where it solidifies in the required form. The 
material is now called Cast Iron. 



METALLURGY OF IRON AND STEEL 



33 



The pig iron is melted in a cupola-furnace. See 
Fig. 4. This consists of a plate-iron shell lined with 
fire-brick and supported upon standards. Double 
doors, Ay opening downward, are closed and held in 




Fig. 4. 



position by a prop, P^ and a sand bottom is rammed 
into place with a slope toward the tapping-hole, T, 
The top of the cupola is open. 

A fan or blower supplies air-blast at a pressure of 



34 MATERIALS OF MACHINES, 

from 5 to lO ounces per square inch. The air enters 
through the pipe B and passes into the furnace by way 
of the chamber C and the openings E, 

The charge is elevated to a platform, indicated at 
Fy and is introduced into the furnace through the 
charging-door D. Kindling and wood are first laid 
upon the sand bottom. Upon this the '' bed " of coke 
is charged, and then alternate layers of iron and coke 
till the level of the charging-door is reached. The fire 
is lighted and the blast turned on. The coke burns, 
and the iron melts; and as the top of the charge settles 
gradually, more iron and coke are ** charged on.'* 

The melted iron collects in the bottom and is drawn 
off periodically at T into a receiving ladle, from which 
it is distributed. Since the hot iron comes in contact 
with the air-blast there is always silica produced by 
the oxidation of some of the silicon. Also a consider- 
able amount of silica sand is introduced into the cupola 
adhering to the pig iron. If the cupola only runs one 
or two hours a day, as in small foundries, the silica 
does not interfere with operation. But for long or 
continuous running it is necessary to include limestone 
with the charge for a flux, and to tap off slag at S, 

After all the iron to be melted has been charged 
into the cupola, the drawing off of melted iron con- 
tinues and the charge settles down till the cupola is 
empty except for slag and a little iron. The blast is 
then slopped, the prop, P, is knocked out, the doors, 



METALLURGY OF IRON AND STEEL. 



35 



A, swing down, and the residue of slag and iron drops 
out. 

Sec. 28. Puddling Process. —Both pig iron and 
wrought iron contain siHcon, manganese, carbon, sul- 
phur, and phosphorus; but in pig iron the sum of these 
is usally from 3 to 10^, while in wrought iron their 
sum does not usually exceed i^. The object of 
puddling is to change pig iron into wrought iron. 
The process must therefore provide means for the 
removal of these substances. The removal is effected 
by oxidation and the puddling process is carried on 
in a reverberatory furnace. This furnace requires 
description. 

See Fig. 5. ^ is a fire-box provided with a grate 




Fig. 5 



upon which solid fuel is burned. H is a hearth in 
which the metallurgical operation is carried on. E is 
a passage connecting with the stack. F is the ash-pit, 
and B and D are doors for the introduction of fuel and 
the material to be treated in the hearth. The material 



36 MATERIALS OF MACHINES, 

in the hearth is heated by the hot gases which pass 
over it, and also by heat reflected from the highly 
heated refractory material of the furnace roof. Solid 
fuel burns on the grate, and the air-supply through 
the ash-pit is under control. If air-supply were just 
sufficient for perfect combustion, the resulting carbon 
dioxide and nitrogen, at a temperature corresponding 
to the calorific intensity of the fuel, would pass over 
the hearth and give up part of their heat to the fur- 
nace walls, and to the material in the hearth, and then 
go on at lower temperature to the stack. But if air- 
supply be more restricted, carbon monoxide will result, 
which will burn in the hearth with air admitted above 
the fire or through the bridge-wall L. In this case 
the fire-box becomes a gas-producer, and the gas 
burns in the hearth. 

The flame which passes over the hearth of this fur- 
nace may be made an oxidizing, a neutral, or a reduc- 
ing flame. Thus, by a free admission of air through 
the fire or about it complete combustion of all carbonic 
oxide is insured, and an excess of oxygen is carried 
over the hearth with the products of combustion. 
This results in a tendency to oxidize materials in the 
hearth. If the admission of air be so regulated as to 
supply only just enough oxygen to complete the com- 
bustion of all carbonic oxide, the flame will be neutral, 
i.e., it will not tend either to give out or to take up 
oxygen. If the air-supply be restricted below the fire, 



METALLURGY OF IRON AND STEEL, 37 

carbonic oxide will result from the incomplete combus- 
tion; and if no air be admitted above the fire this 
carbonic oxide will pass over the hearth with a ten- 
dency to take up oxygen from the materials there, or 
to reduce them. 

In the form of reverberatory furnace used for 
puddling, the bottom of the hearth is made up of cast- 
iron plates which are covered to a depth of about three 
inches with a lining or *' fettling" composed of silica 
and oxide of iron. The fettling is put in as follows: 
Tap-cinder (which may be represented thus: 2FeO, 
Si02) is charged in upon the iron plates, spread evenly, 
and subjected to a temperature high enough to soften 
it in the presence of oxygen. The FeO takes up 
oxygen and becomes Fe203. This will not remain in 
combination with the silica, and hence the fusible 
silicate is converted into infusible ferric oxide and 
silica. Then scrap iron is charged in and subjected 
to an oxidizing flame. It is thereby changed to mag- 
netic oxide, which is raised to a welding heat and 
spread smoothly over the hearth bottom. 

If the hearth were lined with silica, the lining would 
be fluxed away by the ferrous oxide formed during the 
puddling process, with considerable loss of iron. Also 
it is impossible to remove phosphorus in the presence 
of free silica.'^ 

^ See Sec. 32, 



38 MATERIALS OF MACHINES. 

There are two puddling processes: Dry Puddling 
and Wet Puddling. In the first, and less used process, 
white pig iron is heated in the hearth of the reverbera- 
tory furnace and subjected to the action of an oxidizing 
flame. White iron differs from gray iron in passing 
through an intermediate pasty condition before melt- 
ing. During the passage through this condition, the 
iron is constantly stirred with a *' rabble " or iron bar, 
which is inserted through a hole in the door D. The 
order in which oxidation of substances occurs is 
silicon, manganese, carbon, iron. A considerable 
part of the silicon and manganese is oxidized during 
the melting and ferrous oxide also is formed. The 
silica and manganous oxide combine to form silicate 
of manganese, a fusible slag, and if silica is still left 
free it combines with ferrous oxide to form silicate of 
iron or slag. When the silicon and manganese are 
completely oxidized, the oxygen attacks the carbon 
and iron at the surface of the bath of metal. The 
resulting carbon dioxide passes off to the stack, and 
ferrous oxide acts as a carrier of oxygen, i.e., it is 
mixed with the bath and gives up its oxgen to com- 
bine with the carbon of the iron carbide, and the 
result is that carbon monoxide bubbles up to the sur- 
face of the bath and burns there to carbon dioxide, 
while the iron of the oxide and carbide remains in the 
hearth. This continues till the carbon is almost 
entirely removed, Then, because of the raising of the 



METALLURGY OF IRON AND STEEL, 39 

fusing-point, the iron begins to solidify and is collected 
in a '* puddle ball," which is really a sponge of 
wrought iron with its interstices filled with slag. This 
is raised to a welding temperature, and put through a 
^^ squeezer y'' where the slag is squeezed out and the 
component parts are welded together. It is thereby 
converted into a ''bloom." This bloom is then put 
through a ''roughing train" of rolls and is thereby 
converted into "muck bar," which is cut up, piled, 
reheated, welded under a hammer, and rolled into 
*' merchant bar." This piling, heating, and rolling is 
sometimes repeated, with a resulting product of finer 
fibre and increased strength and ductility. 

In wet puddling, the more commonly used pro- 
cess, gray iron is used, and it is allowed to become 
entirely fluid before it is "rabbled." The oxide of 
iron in this process, instead of being formed in the fur- 
nace, is derived from the fettling or introduced in the 
form of "mill scale, "^ or slag from previous heats 
that are rich in ferrous oxide or some kind of rich ore. 

The chief distinction, then, between the two puddling 
pocesses is that in dry puddling the oxygen is supplied 
by the air, while in wet puddling the oxygen comes 
from the oxide of iron which is introduced with the pig 
iron. 

In order that the phosphorus may be removed it is 

* The iron g.j^ide that scales off from iron when it is hammered or 
rolled, 



40 MATERIALS OF MACHINES. 

necessary that there should be an excess of ferrous 
oxide in the fetthng and the slag. Then phosphorus 
is oxidized to PgO^, and this combines with FeO to 
form ferrous phosphate (Fe3P20g). This is the form in 
which the phosphorus appears in the slag. If there 
had been uncombined silica present in the slag the 
phosphoric anhydride would have been reduced again 
to iron phosphide and the phosphorus would have 
appeared in the iron instead of in the slag. 

Sulphur is removed in the puddling process, but the 
manner of its removal is not clearly understood. The 
sulphur exists in the pig iron as iron sulphide, and it 
appears in the slag in the same form. A basic slag 
(i.e., slag with excess of ferrous oxide), and a long 
period of contact of iron with the slag, are favorable to 
the removal of sulphur. 

Sec. 29. A process is sometimes used which is inter- 
mediate between the blast-furnace process and the 
puddling process. It is called refining. It removes 
most of the silicon and manganese, but stops the 
process of removal before the iron becomes too infusi- 
ble to be cast. The furnace for this process is a 
rectangular hearth with tuyeres on two sides bringing 
air under pressure. Melted iron from the blast-furnace 
may be run into this furnace and subjected to the 
oxidizing air-blast, or pig iron may be charged in 
with coke to melt it. In either case iron oxide may 
be introduced to hasten the removal of gilicon and 



METALLURGY OF IRON AND STEEL. 41 

manganese. The iron, after completion of the treat- 
ment, is run out into sand moulds, where it cools in 
the form of plates. These plates are broken up and 
taken to the puddling-furnace, where the conversion 
into wrought iron is completed. The refinery changes 
gray pig iron into white pig iron, because it removes 
the silicon which causes much of the carbon to change 
into graphite during cooling. 

Sec. 30. Processes for Making Tool-steel from 
Wrought Iron. — The difference between wrought iron 
and tool-steel is in the amount of carbon contained. 

Wrought iron has from o. i^ to 0.3^ 
Tool-steel '' '' 0.5^ to 1.5^ 

The change from wrought iron to tool-steel is therefore 
to be effected by addition of carbon. 

Cementation Process. — Bars of very pure wrought 
iron, about f^^ X 5^^ X 12 feet long, are packed in 
refractory boxes about 3 feet wide by 3 feet deep, with 
alternate layers of rather finely divided charcoal. 
These boxes, which are sealed up to exclude the air, 
are in a furnace where the temperature is gradually 
raised to about 3000° F. and maintained for several 
days, and then allowed to cool down. Iron in contact 
with carbon at high temperature tends to absorb carbon 
slowly, and it is found that the bars, after treatment as 
described, are changed to steel. The carbon, how- 
ever, is not uniformly distributed, the structure is 



42 MATERIALS ^OF MACHINES, 

coarse, and the material brittle. This material (called 
blister-steel) is changed to tool-steel by the crucible 
process, as follows: 

The blister-steel is broken up into small pieces and 
charged into refractory crucibles about 2 feet high, 
with an average diameter of about io'\ These 
crucibles are placed in a furnace, usually of the Siemens 
regenerative type, where the melting temperature of 
steel can be attained, and their contents is fused. This 
fluid steel is then cast into an ingot, which is homo- 
geneous chemically, but of coarse, crystalline structure, 
because of its heat treatment. It is then reheated and 
hammered into standard sizes and forms, and the 
mechanical working gives it a fine homogeneous struc- 
ture."^ 

The cementation process is often omitted and 
wrought iron is charged into the melting crucibles 
together with cast iron which is free from sulphur and 
phosphorus. Coke or charcoal may be charged also 
to prevent oxidation at the surface, and to serve as a 
source of carbon. Some carbon may be absorbed from 
the crucibles which contain either plumbago or finely 
divided coke. Either ferro-manganese or spiegel- 
eisen f is introduced into the crucible because the 

* Explained in Chapter IV. 

■f A product of special blast-furnaces which contains iron, carbon, and 
manganese. The manganese is present in percentage ranging from lo 
to 80. With high manganese it is called ferro-manganese. With low 
manganese it is called spiegeleisen. 



I 



MET/ILLURGY OF IRON AND STEEL 43 

manganese reduces any iron oxide that may be present, 
and removes gas or causes it to go into solution, thus 
preventing porosity. The carbon of the ferro or 
Spiegel increases the carbon of the steel. The melter 
regulates these sources of carbon so as to insure close 
approximation to the required grade of the product. 

Sec. 31. The Bessemer Process. — Bessemer steel 
is very similar to wrought iron in chemical composi- 
tion, but usually contains a little more carbon. The 
structure, however, is different, because of the differ- 
ence in the method of manufacture. Thus wrought 
iron is built up from small particles of iron covered 
with slag. The slag is not entirely removed and the 
process of rolling draws out the particles into threads 
that are still surrounded by slag. This gives wrought 
iron the appearance of a fibrous structure. But 
Bessemer steel is cast into a solid ingot and then drawn 
down to the required shape and size. It therefore 
shows the crystalline structure of the iron itself. 

The Bessemer process changes pig iron into steel 
containing from o. i^ to 0.6^ of carbon. This change 
is accomplished in a vessel called a converter. See 
Fig. 6. 

The vessel is made up of riveted iron or steel plates, 
and is lined with ** ganister." ^ The converter is 
mounted upon trunnions. A, A, and can be turned 

* See Section 16. 



44 



MATERIALS OF MACHINES. 



about the axis of the trunnions into any required posi- 
tion. Cold air from the blowing-engine, at a pressure 
of 20 to 25 pounds per square inch, enters at E, follows 
the passage shown to Fy whence it passes into the con- 




FiG. 6. 



verter through holes about f ^^ diameter that pierce the 
conical fire-bricks shown in the converter bottom. 

The Bessemer plant includes cupolas for melting the 
pig iron. The melted iron is conveyed to the con- 
verters either through properly formed channels with 
refractory linings, or in ladle-cars running upon a track. 
Sometimes these cars transport the fluid iron directly 
from the blast-furnace to the converter. 

The converter is turned on its side, and a charge of 
iron is run in. It is then turned into a vertical position 
and a valve opens automatically to turn on the blast, 
and the air is forced through the bath of iron. The 



METALLURGY OF IRON AND STEEL. 45 

results are as follows : The oxygen of the air combines 
with the oxidizable substances of the bath; and iron 
being- in great excess, ferrrous oxide is formed through- 
out the entire '^blow. " But siHcon is also present, 
and the ferrous oxide is reduced by it, and silica is 
formed thus, as well as by direct combination of silicon 
with the oxygen of the air. Manganese is also present 
and oxide of manganese is formed, and this combines 
with silica to form silicate of manganese, a fusible slag. 
If the silica is in excess, some fusible silicate of iron is 
also formed. During this period brilliant sparks of slag 
are thrown from the mouth of the converter. 

When all the silicon and manganese are removed, 
the carbon begins to be oxidized, directly by the 
oxygen of the air, and indirectly by the oxygen of the 
ferrous oxide. Carbon monoxide is formed, which 
passes off from the bath, and on reaching the mouth of 
the converter burns to carbon dioxide in a long, bluish 
flame. When the oxidation of the carbon is complete, 
there is no substance left to reduce the iron oxide 
formed, and reddish fumes appear at the mouth of the 
converter, and the process is immediately stopped by 
turning the converter on its side. 

The converter now contains nearly pure iron, and 
although its fusion temperature is about 4000° F., it 
remains fluid. The fuel which, by its oxidation or 
combustion, has raised the temperature of the con- 
verter from the melting-point of pig iron to that of 



46 MATERIALS OF MACHINES. 

wrought iron, is the silicon, manganese, and carbon of 
the pig iron. 

When the first experiments were made on the 
Bessemer process, it was thought that the blow could 
be stopped at the right point to leave in the amount of 
carbon necessary to make steel ; but it was found im- 
possible to get uniform results, and also it was found 
that the resulting metal was brittle and worthless. 

This was due to the fact that iron oxide remained in 
the metal, and that some gas was occluded, causing 
porosity. To overcome these difficulties, the blow 
is continued till the carbon is completely removed, 
and a known proportion of spiegeleisen or ferro-man- 
ganese is added to effect the recarburization. The 
manganese reduces the iron oxide, and, in some not 
very well understood way, removes the occluded gases 
or causes them to go into solution. After the addition 
of the Spiegel or ferro, the contents of the converter is 
poured out into a ladle, from which it is cast into 
ingots, which are rolled into rails, or plates, or into 
blooms, which are to be rolled or forged into required 
forms. 

Sec. 32. The Basic Bessemer Process. — During the 
blow as described, phosphoric acid and ferrous oxide 
are formed simultaneously, and these combine to form 
phosphate of iron, or ferrous phosphate; thus 3FeO -|- 
P^Og = Fe3P20g. But this is reduced again to iron 
phosphide by silicon and carbon, and therefore little 



METALLURGY OF IRON AND STEEL. 47 

or no phosphorus can be removed until after the com- 
plete removal of these substances from the metal in the 
converter. Ferrous phosphate is also reduced by 
silica, because the silica has greater affinity for ferrous 
oxide than phosphoric acid has, and so ferrous silicate 
is formed and phosphoric acid is left, which is probably 
reduced to iron phosphide by the metallic iron, with 
formation of ferrrous oxide. 

The lining of the Bessemer converter described is 
largely silica, and therefore silica is always present, 
and no phosphorus can be removed in a converter with 
a "ganister" or "acid" lining. It is necessary, 
therefore, to use pig iron for this process which is very 
low in phosphorus, since the presence of phosphorus in 
the product in any considerable amount is very un- 
desirable. 

The fact that a large proportion of the iron ore of 
the world contains phosphorus, which is not removed 
in the blast-furnace, made it desirable to find a way to 
eliminate phosphorus in the steel-making process. 
This led to the invention of the Basic Bessemer 
Process, in which a lining of lime and magnesia is sub- 
stituted in the converter for ganister. The only free 
silica, then, is that which results from the oxidation of 
the silicon in the pig iron. This combines with the 
lime or magnesia of the converter lining, or with 
that which is charged into the converter during the 
blow, and forms a stable slag, the sihca being 



4S MATERIALS OF MACHINES. 

thereby rendered powerless to reduce the ferrous 
phosphate. 

The hme or magnesia present then replaces the 
ferrous oxide of the ferrous phosphate, forming cal- 
cium or magnesium phosphate, which is probably the 
form in which the phosphorus cliiefly exists in the 
slag. 

In the acid process iron is not usually used which 
contains less than 2fo of silicon, because the com- 
bustion of at least that amount of silicon is necessary 
to produce a sufficiently high temperature in the con- 
verter. 

In the basic process silicon is an undesirable ele- 
ment, since all the silica produced must be neutralized 
by lime, in order that the process shall succeed. For 
this reason iron with 0.5^ silicon is best, and 1.5^ is 
the highest allowable limit. This makes it necessary 
to substitute some other fuel, and therefore pig iron 
high in manganese is used. The phosphorus is also a 
fuel and raises the temperature during the ' ' after- 
blow. '' In the basic process little or no phosphorus 
is removed till after the complete removal of the 
carbon, and the blow has to be continued after the 
*' dropping'' of the carbon flame. The duration of 
the afterblow is determined from a knowledge of the 
amount of phosphorus in the pig iron used, or by 
taking samples at intervals during the afterblow and 
making physical tests. 



i i 



a a 



METALLURGY OF IRON AND STEEL, 49 

The best pig iron for the basic process contains: 

P, about 3 per cent 

Mn, over 2 

Si, 0.5 

S, less than o.i ** *' 

This is white iron, because of high manganese and low 
sihcon, whereas the high siHcon iron used in the acid 
process is gray. 

Sec. 33. Control of Temperature in the Bessemer 
Converter. --Either too high or too low temperature of 
the steel at pouring results in porosity, and therefore 
this temperature must be carefully regulated. If iron 
too high in silicon be used in the acid process, too high 
temperature results, and conversely. 

In the basic process the difficulty is usually to keep 
the temperature high enough. If the temperature is 
too high, it may be reduced by charging in scrap-steel 
from the mill, which is thus remelted, absorbing sur- 
plus heat, and is rendered available for use. The 
temperature is also sometimes reduced by admitting a 
small amount of steam into the blast-pipe. 

If the temperature becomes too low, the converter 
may be inclined, as shown in Fig. 7, during the burn- 
ing out of the carbon. When the converter is vertical 
the carbon monoxide formed burns at the mouth of the 
converter, and the heat evolved is lost as far as raising 
the temperature of the inside of the converter is con- 



so 



MATERIALS OF MACHINES. 



cerned. In the inclined position, however, part of the 
air of the blast passes through the metal bath and 
forms carbon monoxide, and part passes through the 
uncovered tuyere holes and furnishes oxygen to the 
carbon monoxide, and carbon dioxide is formed; i.e., 




Fig. 7. 

combustion occurs inside of the converter, and the heat 
developed raises the temperature of the metal bath. 

Sec. 34. Graphical Representation of the Basic 
Bessemer Process. — Fig. 8 is copied from Wedding's 
'' Basic Bessemer Process," ^ page 143. The diagram 
is plotted from the results of experiments and shows 
the history of a blow in a basic converter. Horizontal 
distances from O represent time, each division corre- 
sponding to one minute. Vertical distances from 
represent percentages of the substances to be removed. 
Therefore the curves represent the change in per- 
centage of the substances during the blow. 

* Translated by Phillips and Prochaska. E. & F. N. Spon, Publishers, 
London. 



METALLURGY OF IRON AND STEEL. 



51 



The silicon is reduced very rapidly from 1.2^ at the 
beginning of the blow; and after six minutes only o.ifo 
remains. From this point on the silicon is slowly 
reduced to zero. 

The manganese is reduced less rapidly than the 
silicon, changing from i .05^ at the beginning to o. 1 5^ 
after nine minutes. It then remains nearly constant 





1 2 3 i , 


TIME, MINUTES.. 
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during the carbon reduction, and then becomes less 
than o. i^. 

There is but little change in the carbon until most 
of the silicon is removed and then the curve drops 
rapidly, and the removal is practically complete in 
sixteen minutes. Up to this time there has been little 
change in the phosphorus. This is of course because 



52 MATERIALS OF MACHINES. 

the ferrous phosphate is reduced by carbon. From 
this point the removal of phosphorus is very rapid, 
being practically complete after the blow has continued 
twenty minutes. 

The curve of sulphur was shown on the original 
diagram, but it was not copied, as the quantity of sul- 
phur remained nearly constant, its value being less 
than o. i^. The blow ends at the twenty-minute line, 
and the curves beyond show the effect of introducing 
spiegeleisen. 

Sec. 35. Fig. 9"^ gives the history of an acid 
Bessemer blow. The amount of silicon is very low for 
the acid process. Phosphorus remained practically 
constant at o.i^, and sulphur at 0.06^. Figs. 8 and 9 
are plotted on the same scale for comparison. The 
blow ends at 9m. los., and the rest of the curve results 
from the introduction of spiegeleisen. 

Sec. 36. Open-hearth Processes. — Steel is also 
made from pig iron in the hearth of a Siemens regen- 
erative furnace. See Fig. 2. The silicon, manganese, 
and carbon are removed by oxidation, as in the pud- 
dling, or in the Bessemer, process. Two processes 
are carried on in open-hearth furnaces: first, Siemens, 
or ''pig and ore," process; second, Siemens-Martin, 
or ''pig and scrap," process. These correspond to 



* Plotted from experiments of F. Julian at South Chicago works of 
Illinois Steel Company. See H. M. Howe, Journal Iron and Steel 
Institute, Vol. II, 1890, page 102. 



METALLURGY OF IRON AND STEEL. 



53 



wet and dry puddling; the difference being that here 
the temperature is high enough so that the product is 
held fluid and cast into an ingot, while in the puddling 





TIME, MINUTES. 
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process the temperature is such that the product 
solidifies and must be treated by rolling-mill processes. 
In the Siemens process pig iron is charged into the 
hearth and melted, part of the silicon and manganese 
being oxidized during the melting, and then rich ore 
is added to supply the oxygen to combine with the 
remaining siHcon and manganese, and the carbon of 
the iron carbide. When the action is complete the 
bath of nearly pure iron is recarburized by the addition 
of spiegeleisen or ferro-manganese, and the man- 
ganese reduces the ferrous oxide present, and removes 



54 MATERIALS OF MACHINES. 

occluded gases or causes them to be dissolved as in the 
Bessemer process. 

In the Siemens-Martin process pig iron is charged 
into the hearth, and melted with partial removal of the 
silicon and manganese, and then steel scrap is charged 
into the bath, which melts, and thus the percentage of 
silicon, manganese, and carbon is reduced by dilution. 
The remaining part of these substances is removed by 
the direct action of the oxidizing flame, and the in- 
direct action of the ferrous oxide formed at the sur- 
face of the bath, and mixed with it. Spiegel or 
ferro are added as in the Siemens process. Ferro- 
silicon and ferro-aluminum are sometimes used in place 
of ferro-manganese for the recarburization, and the 
removal of iron oxide and the prevention of porosity. 

Either acid or basic lining may be used in the fur- 
nace in which the open-hearth processes are carried 
on. With the acid lining no phosporus is removed 
and hence low-phosphorus pig must be used. With 
the basic lining the phosphorus is removed as in the 
basic Bessemer process. 

Sec. 37. Ductile Castings. — Many machine mem- 
bers of somewhat complicated form need to be of 
materal whose ductility and resilience are high. If 
such parts were to be made in large numbers, they 
could be produced by the process of casting much 
cheaper than by the process of forging. For this 
reason much attention has been given to the produc- 



METALLURGY OF IRON AND STEEL, 55 

tion of castings of ductile material. The most impor- 
tant resulting processes are those for the production of, 
first, Malleable Castings; second, Steel Castings. 
Some of the grades of trass and bronze give castings 
which are strong and ductile, but the high cost puts 
them out of competition for many purposes. 

I. The process for the production of Malleable 
Castings. — White cast iron, i.e., iron with all the 
carbon in combination, is melted and cast into the 
required forms. These castings, which are hard, 
weak, and brittle, are packed in cast-iron boxes in the 
midst of coarsely powdered oxide of iron, usually 
haematite ore or hammer-scale. These boxes are 
sealed and exposed to a temperature of full redness in 
a reverberatory oven for from three to six days. They 
are then slowly cooled down, and the cast iron is 
changed to something that is very much like wTought 
iron in strength, ductility, resilience, and softness. 

There are two reasons for this change: first, the 
total carbon is reduced; and second, the combined 
carbon is nearly all changed to very finely divided 
graphitic carbon. 

The following analyses "^ show these changes : 

Total Graphitic Combined 

Carbon. Carbon. Carbon. 

Before mallifying. . 2.79^ 0.177^ 2.613^ 
After mallifying. . . 1.74^ 1.565^ 0.175^ 

* Analyses made by Mr. W. H. McCord at the chemical laboratory 
of Stanford University. 



56 MATERIALS OF MACHINES, 

The iron for the castings was melted at first in 
cupolas, with very little chemical change. But it was 
found desirable to have the total carbon as low as 
consistent with the retaining of suifificient fluidity for 
making satisfactory castings. Hence a reverberatory 
furnace was substituted for the cupola. The iron is 
melted down in the hearth, and subjected to an oxidiz- 
ing flame until its carbon is reduced to the allowable 
minimum, and then it is cast. Because of this change 
the process became applicable to much larger castings. 
The chief function of the mallifying process in large 
castings is probably to change combined carbon to 
graphitic carbon. 

The reduction of total carbon is sometimes accom- 
plished by dilution; i.e., scrap steel or wrought iron is 
charged in with the pig iron. 

2. Steel Castings. — The melted steel of the open- 
hearth or of the Bessemer converter is often poured 
into moulds of very refractory sand, and the resulting 
castings are called steel castings. Since the *' freez- 
ing-point " of these castings is about 1000° F. above 
that of cast iron, the ill effects of shrinkage are greater. 
Moreover, steel castings are of coarse structure because 
they are cooled from the fluid state; and to render the 
structure fine, and the castings strong and ductile, it is 
necessary to anneal them very carefully. 



METALLURGY OF IRON AND STEEL. 



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CHAPTER 11. 
TESTING. STRESS-STRAIN DIAGRAMS. 

Sec. 38. The testing of materials, and the methods 
of recording and interpreting results, will be briefly 
considered, as a preliminary to the study of the physical 
qualities of materials. 

A test-piece of proper dimensions may be made of 
any material, and may be broken by the application of 
a force producing tensile, compressive, torsional, or 
transverse stress. It will be assumed that means are 
provided for the application of forces of known value; 
also that any deformation of the test-piece may be 
accurately measured. Let a tension test be considered. 
The force in this case is applied so that it tends to 
elongate the test-piece. The elongation which results 
is called strain. The action and reaction between 
adjacent portions of material is stress. Strain is 
always the deformation which accompanies stress. 

It will be found that for every increment of stress 

there will be an increment of strain. In the early part 

of the test these will be proportional to each other; 

58 



TESTING. STRESS-STRAIN DIAGRAMS, 59 

i.e., stress is proportional to strain. This is Hookers 
Law. After passing a certain limit it is found that 
this proportionality ceases, the increment of strain 
becoming much greater for a given increment of 
stress. This limit is called the elastic limit of the 
material. 

If, before reaching this limit, the stress is gradually 
reduced to zero, the strain will become zero; i.e., the 
test-piece will return to its original dimensions. This 
shows that the material is perfectly elastic, since 
elasticity is the quality of returning to original 
dimensions on the relief of stress* If, however, the 
elastic limit be passed before the relief of stress, the 
test-piece will be permanently elongated. This per- 
manent elongation is called ^^ set/* or permanent 
strain. The strain which disappears on relief of stress 
is called elastic strain. 

If the test be continued, the ratio of stress to strain 
continually decreases after passing the elastic limit. 
After a while a point is reached where no further 
increase of stress can be made, because every effort to 
increase stress is met by so great yielding. The stress 
at this point is called maximum stress, and it repre- 
sents the breaking or ultimate strength of the 
material. From this point on there is an increasing 
strain and a decreasing stress, i.e., the force that is 
sufficient to produce rupture is a decreasing one. 

Up to the time of reaching the maximum stress, all 



6o MATERIALS OF MACHINES, 

units of length of the test-piece share the elongation 
equally. If the piece were of absolutely equal strength 
in all sections, it would continue to elongate equally 
throughout, and would finally yield in all sections at 
once. This is of course impossible, and the point of 
maximum stress is really the point at which some 
local weakness is developed, and where a localization 
of strain occurs; i.e., the test-piece ''necks down," 
and from that point on till rupture the elongation 
occurs in the neck, because the unit sU^ess becomes 
greater with the local reduction of cross-sectional area. 
This does not occur in brittle materials, but stress 
increases from the beginning of the test till rupture 
occurs. 

The test may be made continuous from the beginning 
without relief of stress, and if periodical readings of 
stress and corresponding strain be taken, these 
variables may be plotted with reference to rectangular 
axes, and a curve drawn through the points thus 
located will be the stress-strain diagram of the 
material. The test described is that of a ductile 
material, and B, Fig. \oa, may represent the resulting 
stress-strain diagram. A brittle material gives a 
diagram entirely different in character. Thus C, Fig. 
\ob^ may represent a stress-strain diagram of cast iron. 
If diagrams of different material are plotted on the 
same scale, their physical qualities may be compared 
by inspection of the diagrams. 



TESTING. STRESS-STRAIN DIAGRAMS 



6i 




62 MATERIALS OF MACHINES, 

Sec. 39. The physical qualities which appear on the 
stress-strain diagram are as follows: 

1. Strength at elastic hmit; 

2. Strength, ultimate; 

3. Ductility; 

4. Stiffness. 

5. Elasticity; 

6. Resilience, elastic; 

7. Resilience, ultimate. 

Strength at elastic limit is measured by the stress 
per unit of cross- sectional area of the piece when the 
proportionality of stress and strain ceases. Ultimate 
strength is measured by the stress per unit of cross- 
sectional area when the yielding becomes so great that 
no addition can be made to the stress. Ductility is 
the quality of being drawn out under stress, and is 
therefore proportional to the strain, and to the length 
of the stress-strain diagram on the axis o{ X, Stiffness 
is the quality of resisting yielding or strain, within the 
elastic limit. It is therefore measured by the angle 
which the Hooke's law line makes with the axis of Jf.* 
The greater this angle the greater the stiffness of the 
material. Elasticity is already defined as the quality 
because of which a material regains its original dimen- 



* In using this angle as a measure of stiffness the scales for plotting 
stress and strain must be considered, and diagrams must be plotted on 
the same scale if they are to be compared. 



TESTING. STRESS-STRAIN DIAGRAMS. 



63 



sions on the relief of stress. Resilience is the term 
used to express work done in carrying the test to any 
point. Thus elastic resilience is the work done in 
straining a piece of material to its elastic limit. Ulti- 




FiG. 10^. 

mate resilience is the work done in breaking a piece. 
Since resilience is the work done in producing strain 
in material, it is therefore a measure of the shock- 
resisting power of the material, i.e., it is proportional 
to the energy of a shock or blow which would produce 



64 MATERIALS OF MACHINES. 

the same result. Since the ordinates of the stress- 
strain diagram represent force and the abscissas repre- 
sent the space through which the force acts, it follows 
that the area of the diagram represents work. If, 
then, a perpendicular be dropped from the elastic limit 
of the diagram to the axis of X, a triangle will be 
formed whose area is proportional to the elastic resili- 
ence of the material. Thus in Fig. lob the triangle 
OEH is a measure of the elastic resilience of the 
material represented by the curve B, and the triangle 
OE' K is a measure of the elastic resilience of the 
material represented by the curve A, If a perpendic- 
ular be dropped to the X-axis from the end of the 
diagram, the area bounded by this perpendicular, the 
curve of the diagram, and the axis of X, will be a 
measure of the ultimate resilience of the material. 
Let a comparison of all of these qualities be made for 
the materials represented by the diagrams of Fig. \oa. 
The curve C rises with a continuous curvature; there 
is no straight part denoting a period of proportionality 
of stress and strain; or, in other words, there is no 
elastic range. There is also no limit of elasticity. If 
stress were discontinued at F,^ the curve would not 
return upon itself, but would follow an approximate 
straight line to G, some point to the right of 0. This 
indicates that there is a permanent strain or *^set'* 
whose value is OG on the scale assumed for plotting 

* See Fig. \ob. 



TESTING. STRESS-STRAIN DU GRAMS. 65 

strains. A similar effect would be shown if the stress 
were relieved at any point in the curve. The material 
represented by this curve is therefore imperfectly elas- 
tic. The same is true of the curve i?, which represents 
copper. The straight initial portion of the curves A 
and By however, indicates perfect elasticity.^ 

The elastic strength of the material of A, Fig. 10a y 
is greater than that of B in the ratio of the ordinate 
E^K to EH, C and D have no elastic limit, and 
therefore no value of elastic strength can be assigned. 
The ultimate strength of A is measured by the ordinate 
MN\ of B by M'P'y of C by M"L\ and oi D by 
M'^'Ry and the comparison is easily made. 

The ductility of A is measured by OS^ \ of B by 
0T'\ ofChyOL; andofBhy 0V\ 

The elastic resilience of A is measured (Fig. 10^) by 
the area OE'K\ of B by OEH, No elastic resilience 
can be assigned to C and Dy since they have no 
elastic limit. 

The ultimate resilience of A is measured by the area 
OE'MSS'\ of ^ by the area OEM'TT'\ of C by the 
area OFM"L'y and of D by the area ODM'"VV\ 
Stiffness, being proportional to the angle of the initial 
part of the curve with the axis of X, is in the following 

* It probably is not absolutely true that this material is perfectly 
elastic. By means of very refined measuring apparatus it is found that 
nearly all materials take some "set," even when subjected to compara- 
tively small stress. The values, however, are so minute that they may 
be safely disregarded in the selection of materials for machine parts. 



(>(> MATERIALS OF MACHINES, 

order, beginning with the stiffest material: 1st, A\ 2d, 
B', 3d, i^; 4th, C. 

If a material be tested in compression as well as in 
tension, both stress and strain will be reversed, and 
stresses will be plotted below the axis of X, and strains 
will be plotted toward the left from the axis of F. In 
Fig. lOUy CC and BB' are stress-strain diagrams of 
cast iron and wrought iron, both in tension and com- 
pression. The compression curve of the wrought iron 
is almost identical with the tension curve, up to and 
past the elastic limit. A ductile material cannot, 
however, be tested to rupture in compression, as the 
material either '^buckles," splits parallel to the axis 
of the test-piece, or else simply flattens out, thus 
exposing a constantly increasing area of section to the 
crushing force. A brittle material breaks in compres- 
sion by shearing on planes at an angle of about 45° 
with the axis of the test-piece. The diagram shows 
that cast iron is a much stronger material in compres- 
sion than in tension. 

Stress-strain diagrams may be also plotted from the 
data of torsion and transverse tests, as well as from 
those in which the stress is tensile or compressive. 



CHAPTER III. 

CAST IRON. 

Sec. 40. Cast iron, as previously stated, is com- 
posed of iron, carbon, silicon, manganese, sulphur, 
and phosphorus. Wrought iron has usually the same 
qualitative composition, but the substances other than 
iron are reduced to the very lowest limit possible com- 
mercially. The percentage range of these substances 
in wrought and cast iron is shown in the following 
table: 

Cast Iron. Wrought Iron. 

Graphitic carbon 1.85 to 3.25 

Combined carbon 15 to 1.25 .02 to .25 

Total carbon 2.0 to 4.5 

Silicon 15 to 5. o to .3 

Manganese o to 1.5 o to .3 

Sulphur o to .5 o to .015 

Phosphorus o to 1.3 o to . 15 

Although the only chemical difference is in the 
amount of these substances present, yet the physical 
qualities are entirely different, as is evident from in- 
spection of curves C and B, Fig. loa. B may repre- 
sent wrought iron, and C may represent cast iron. In 

the change from wrought to cast iron the material, in 

67 



68 MATERIALS OF MACHINES. 

tension, has become weaker, less elastic, less stiff, less 
ductile, and less resilient; in compression it has become 
stronger. It would seem that it had become in all 
respects, except for resisting compression, a less 
desirable material for use in machine parts. But there 
is one quality, of which there is no record on a stress- 
strain diagram, because of which cast iron is invaluable 
for many machine parts. It is the quality of fusing at 
a temperature attainable in the foundry cupola. 
Because of this quality it may be cast into sand 
moulds, taking required irregular shapes, which cannot 
be produced by forging; and, after a pattern is once 
made, a large number of duplicates can be easily and 
cheaply produced. Where cast-iron machine members 
are ** stress members," the deficiency in strength is 
compensated by increased cross-sectional areas. Cast 
iron melts at a temperature of about 2500° F. , while the 
temperature of fusion of wrought iron is about 4000° F. , 
or the highest temperature attainable in the Siemens 
regenerative furnace. Wrought iron cannot, there- 
fore, be cast (except by special means), and hence has 
to be shaped by forging. Cast iron cannot be forged 
at all. 

Sec. 41. The carbon in cast iron is usually present 
in two forms : a part is combined or in solution with 
the iron, and a part is in the form of crystals of 
graphite distributed throughout the mass of the iron. 
The reason for this is as follows : When cast iron is in 



CAST IRON. 69 

a fluid state it has a certain capacity for taking carbon 
into solution. This capacity is very much reduced 
when the iron begins to sohdify. If, therefore, the 
fluid iron has absorbed more carbon than it is capable 
of holding when it is solidifying, the excess will 
crystallize out as graphite; and, since this crystalliza- 
tion occurs after the iron has ceased to be wholly fluid, 
the graphite crystals remain suspended m the iron, 
notwithstanding their less specific gravity. 

Sec. 42. The blast-furnace produces different grades 
of cast iron, which are numbered usually from No. I 
to No. 6. No. I is very gray at the fracture, and 
contains a large amount of graphite. No. 6 is white 
at the fracture, and all the carbon is in the combined 
state. The intermediate numbers represent the grada- 
tion from one to the other. The total carbon in cast 
iron depends chiefly upon the type and conditions of 
working of the furnace. The distribution of the total 
carbon between combined carbon and graphite is 
dependent upon the relative amounts of the other sub- 
stances present and upon the rate of cooling. The 
amount of total carbon may also be influenced by the 
presence of the other substances. 

Sec. 43. Cast iron depends for its physical qualities 
upon the effect of the silicon, manganese, carbon, sul- 
phur, and phosphorus with which it is mixed or com- 
bined, and also upon the effect of these substances 
upon each other. 



70 MATERIALS OF MACHINES. 

The effect of graphitic carbon upon cast iron is to 
make it weak, both in tension and compression, and to 
reduce its ductihty. This effect is probably due to the 
fact that the presence of the crystals of graphite inter- 
rupts the continuity of the iron structure. Graphitic 
carbon also renders the iron softer ; probably because 
of the introduction of a softer material, and because 
the introduction of graphitic carbon is usually at the 
expense of the combined carbon, which hardens the 
material. 

The increase of combined carbon in pure iron con- 
verts it, first into soft steel, then into tool-steel, and 
finally into white cast iron. The change from pure 
iron to steel with i^ carbon is accompanied by steadily 
increasing strength and steadily decreasing ductility. 
The change from steel with i^ carbon to white cast 
iron is accompanied by reduction both of strength and 
ductility. 

In Fig. lOa, B maybe taken to represent the stress- 
strain diagram of pure iron. The gradual increase of 
carbon would gradually change it into a material 
represented by the stress-strain diagram A, the 
strength being increased from PAI' to NM, while the 
ductility is reduced from OT^ to 0S\ The compres- 
sive strength and ductility would be similarly changed. 
After passing i ,ofo carbon, the addition of further 
amounts of carbon decreases the tensile strength, still 
further decreases ductility, and increases the compres- 



CAST IRON. 71 

sive strength. In Fig. loa, the stress-strain diagram 
A, which may represent steel with ifo carbon, is, by- 
gradual increase of carbon, converted gradually into 
the stress-strain diagram C, which may represent 
white iron. It follows, then, that the effect of com- 
bined carbon on cast iron is to decrease tensile strength 
and ductility and resilience, and to increase compres- 
sive strength and ductility and resilience. The effect 
of combined carbon is greater in degree than that of 
graphitic carbon, i.e., o.ifo of combined carbon makes 
changes that are greater in amount than those made 
by o,ifo of graphitic carbon. If an iron be selected 
having a certain total carbon (say 3.5^, which is about 
the average for foundry use), and if all this carbon be 
in the form of combined carbon, i.e., no graphitic 
carbon present, the selected iron will be a brittle, hard 
material, weak in tension and strong in compression. 
If now a part of the combined carbon be converted into 
graphitic carbon, the result will be as follows: The 
tensile strength and ductility and resilience will be 
increased, because the reduction of combined carbon 
has increased these qualities, and the increase of 
graphitic carbon has reduced these qualities, but the 
reduction is less than the increase, because the effect 
of the graphitic carbon is less in degree than that of 
the combined carbon, and the resultant effect is an 
increase of tensile strength and ductility. The com- 
pressive strength, ductih'ty, and resilience are decreased 



72 MATERIALS OF MACHINES, 

because both the decrease of combined carbon and the 
increase of graphitic carbon tend to produce that result. 
The material is rendered softer by the reduction of 
combined carbon and the increase of graphitic carbon. 
Since this change has increased tensile resilience, it 
follows that the tensile shock-resisting power of the 
material is increased, while the compressive shock- 
resisting power is decreased. The reversal of this 
process would, of course, produce reverse results. If 
control of the distribution of total carbon between 
graphitic carbon and combined carbon were possible, 
it would become possible to control, at least in part, 
the qualities of castings so as to fit them for different 
purposes. 

The effect of this conversion of combined carbon into 
graphite is strikingly illustrated in the process of 
mallifying white-iron castings.^ The process converts 
the combined carbon of the white iron into the very 
finely divided graphitic carbon of the malleable cast- 
ings. The result is the conversion of weak, hard, 
brittle material into strong, soft, ductile material. 

Sec. 44. The rate of cooling of castings has a very 
marked effect upon the crystallizing out of tke graphitic 
carbon. Suppose iron with a low total carbon to be 
melted and cast into a mould, a part of whose internal 
surface is of sand, and another part of iron. The part 
of the melted metal which comes in contact with the 

* See Sec. 37. 



CAST IRON, 73 

iron surface will be ^* chilled," i.e., cooled far more 
rapidly than the part which comes in contact with the 
sand surface (because of the greater conductivity of the 
iron). The chilled part of the casting will be white in 
fracture, showing that the carbon is all in combination, 
while the other parts of the casting will be somewhat 
gray, showing that a part of the carbon has crystallized 
out as graphitic carbon. The reason for this effect is 
that the crystals of graphite need some time to form, 
and since the sudden cooling does not allow this time, 
the carbon all remains as combined carbon. 

For certain purposes castings are required with por- 
tions of their outside surface very hard to resist wear, 
while the body of the casting needs to be strong, 
ductile, and resilient, to resist rupture by shock, and 
soft so that it may be finished. 

A casting with gray-iron body and with white iron 
at the wearing surface would fulfil these requirements. 
Such castings are made by chilling the wearing surface, 
as in case of car-wheels, chilled rolls for iron-mills, 
etc. 

Sec. 45. In homogeneous castings carbon distribu- 
tion may be controlled by regulating the amount of 
silicon and manganese present. 

If gray iron, low in silicon, be melted, and if man- 
ganese be added to it,^ the fracture of the cooled 

* This may be done by adding ferro-manganese. 



74 MATERIALS OF MACHINES. 

material will be whiter, showing that some graphitic 
carbon has been converted into combined carbon. 

If white iron low in manganese, sulphur, and phos- 
phorus be melted, and if silicon be added to it,"^ the 
fracture of the cooled material will be grayer, showing 
that some combined carbon has been converted into 
graphitic carbon. Therefore the presence of man- 
ganese tends to increase the capacity of iron to hold 
carbon in combination, while the presence of silicon 
tends to decrease this capacity. 

The presence of sulphur or phosphorus also affects 
the distribution of carbon. Both tend to increase the 
amount of combined carbon. If these elements are 
introduced in any considerable quantity, they render 
the iron unsafe for stress members of machines, and 
especially those subjected to shock. Sulphur should 
not exceed o.is^, and phosphorus should not exceed 
0.3^. These elements, therefore, cannot be used for 
regulating the carbon distribution. The ill effects, 
however, which result from the use of silicon or man- 
ganese for this purpose are comparatively small. 
Mr. T. Turner, of Mason College, Birmingham, made 
a series of experiments to determine the effect of silicon 
upon cast iron.t 

He used iron which had a total carbon as nearly as 
possible 2^, and with sulphur, phosphorus, and man- 

* This may be done by adding ferro-silicon. 

f See Iron (The Metallurgy of), T. Turner, page 192. 



CAST IRON, 



75 



ganese quite low; and, by means of ferro-silicon, added 
successively increasing amounts of silicon, and then 
subjected the products to chemical and physical tests. 
The results of these tests as to tensile and compressive 
strength and hardness are plotted in Fig. ii. At first 




9 10 — fc SILICON 



progress toward the right along the axis of X from 
corresponds to conversion of combined carbon into 
graphitic carbon. It has been already stated that this 
conversion reduces compressive strength. But the 
curve of compressive strength rises to o.Sfo silicon. 



7^ MATERIALS OF MACHINES. 

Mr. J. W. Keep has pointed out to Mr. Turner that 
white iron often does not cast solid, but has blow-holes 
that decrease strength; and that a small amount of 
silicon produces sound castings.*^ It may therefore be 
that this is the first effect of silicon, and this would 
account for the rise of the curve. From 0.8^ silicon 
to 4^ silicon the curve of compressive strength falls 
rapidly, and then less rapidly till the end of the range. 
The curve of tensile strength rises from o.ofo silicon to 
1.9^ silicon and then falls gradually to the end. 

The softest mixture is between 2fo and 3^ silicon. 
No data are given to show ductility, and hence no 
curve of resilience can be plotted. It is probable, 
however, that the curve of tensile resilience would fol- 
low approximately the curve of tensile strength, and 
that the curve of compressive resilience would follow 
approximately the curve of compressive strength. 

Sec. 46. A varied quality of product is required from 
a foundry. Some castings are not subjected to any 
considerable stress, and the main requirement is that 
they shall be soft and **run sharp'*; i.e., that they 
shall take accurately the form of the mould. The 
crystallizing out of the graphite causes a reduction of 
the shrinkage of the iron in cooling. This result might 
reasonably be expected, since the formation of 
graphite, whose specific gravity is much lower than 

* Probably, as in case of steel, by increasing the capacity of iron to 
absorb gas. 



C/IST IRON. 77 

that of iron, must reduce the specific gravity of the 
whole mass, i.e., a given weight of graphitic iron 
would occupy a larger cubic space than if the carbon 
were all combined. This, in part, counteracts the 
effect of the natural shrinkage of the iron, and so the 
castings fill the mould better. Iron with a large pro- 
portion of graphitic carbon is most satisfactory for soft, 
sharp castings. This means iron with a large propor- 
tion of silicon. Fig. 1 1 shows, however, that for 
maximum softness silicon should not exceed 3^. 

Other castings require to be as strong as possible in 
tension, and yet soft enough to be worked economically 
in the machine-shop, and also hard enough to resist 
wear. The maximum tensile strength coincides with 
almost the softest iron at 2^ sihcon. It is better to 
sacrifice something of tensile strength to gain in hard- 
ness and compressive strength, and hence about 1.5^ 
silicon would probably be best for machine castings. 
If a casting were required capable of withstanding 
severe compressive shocks, as, for instance, an anvil- 
block for a steam-hammer, then, since very little 
machine finishing needs to be done upon it, a material 
should be selected with greater compressive strength, 
although the hardness is much greater. 

If castings are required for ** chilling'* or for the 
process of malleableizing, they must be very low in 
silicon, as the presence of any very considerable 
amount of the graphitic carbon is fatal to the success 



78 MATERIALS OF MACHINES. 

of either process. The presence of manganese is 
helpful here as tending to produce white iron. 

The set of curves in F'ig. 1 1 will serve for a partial 
guide in the mixing of grades of iron for the production 
of any kind of castings. The following points must 
be kept in mind, however: 1st. That these results 
cannot be produced by means of silicon if any consider- 
able amount of manga^iese, sulphur ^ or phosphorus is 
present. 2d. It is probable that these curves would 
have been modified if iron with an average total carbon 
had been used, say 3.5^, instead of 2^. Silicon seems 
to influence the physical qualities of iron {ft) because 
of its effect on the distribution of the carbon ; (b) 
because of its effect upon the iron itself. The former 
is a desirable effect, increasing strength, ductihty, and 
softness, while the latter is an undesirable effect, 
resulting in decreased strength and increased hardness. 
In Fig. II evidently the influence upon carbon pre- 
dominates in the early part of the series, i.e., from o^ 
silicon to about 2.5^ silicon; while the direct influence 
upon the iron predominates from 2.5^ silicon to the 
end of the series. If the total carbon had been 
greater, the predominance of the influence of the 
silicon upon the carbon might have extended further in 
the series. 

Sec. 47. Machine castings of high strength are pro- 
duced by charging about 25^ of steel scrap with the 
pig iron. This reduces the total carbon by dilution, 



CAST IRON. 79 

and the resulting iron has the graphite very fine and 
evenly distributed. The castings are soft, and easily 
worked, and yet have about 50^ greater strength than 
the same iron without the addition of steel. 

The effect of this treatment is quite similar to the 
effect of the mallifying process."^ Thus the total 
carbon is reduced and the graphitic carbon is very fine 
and evenly distributed. 

Sec. 48. In foundry practice it is desirable that a 
large amount of ** scrap" be used; partly because 
** gates," ^* risers," etc., are a necessary product of 
every heat, and partly because a good deal of scrap is 
offered for sale at a low price. The effect of remelting 
iron is to harden it, and therefore scrap is always of 
harder grade than the ' * pig ' ' from which it was orig- 
inally cast. 

The hardening effect of remelting is very clearly 
shown by some experiments made at the Gleiwitz 
foundry in Silesia, and quoted by M. Ferd. Gautier in 
a paper read before the Iron and Steel Institute (see 
Journal of 1886). The results are given in the follow- 
ing table : 

Original After After 

Pig Iron. Fourth Casting. Sixth Casting. 

Graphitic carbon 2.73 2.54 2.08 

Combined *' 0.66 0.80 1.28 

Total " 3.39 3.34 3.36 

Silicon 2.42 1.88 1. 16 

Manganese 1.09 0.44 0.36 

Sulphur 0.04 o. 10 o. 20 

Phosphorus 0.31 030 0*30 

* See Sec. 37. 



3o MATERIALS OF MACHINES. 

Thus the six successive meltings resulted in a 
decrease in the amount of silicon and manganese, and 
an increase in the amount of sulphur. (This latter 
probably absorbed from the fuel.) Graphitic carbon 
is decreased and combined carbon is increased; there- 
fore the combined effect of decrease of silicon and 
increase of sulphur was greater than the effect of the 
decrease in manganese. The change necessary to 
convert this again into soft gray iron is the addition of 
silicon, provided the amount of sulphur is not too 
great. The reasons for the hardening effect of remelt- 
ing are : {a) the reduction of the silicon, resulting in 
the redistribution of carbon; (J?) the increase of sul- 
phur. Of the substances which are found in combina- 
tion with iron, silicon is first oxidized, manganese 
being next in order. Therefore, when iron is melted 
in the presence of an air-blast, some of the silicon is 
always oxidized, and usually some of the manganese. 
Iron is melted in the presence of anthracite coal or 
coke, and hence there is the possibility of absorption 
of sulphur. If the total carbon is sufficiently high, the 
softening of iron can be accomplished very satisfactorily, 
by the addition of a proper amount of ferro-silicon, 
which usually contains about lofo of silicon. But if 
total carbon is low, pig iron high in silicon and carbon 
would serve better, because it would carry a larger 
amount of carbon per unit of silicon. 

Sec. 49. '* Burnt scrap" is cast iron which has 



CAST IRON. 8 1 

been exposed during use to the action of oxygen at 
high temperatures; as, for instance, old grate-bars, 
silt-kettles, etc. A portion of the iron becomes iron 
oxide. If such iron be melted, the iron oxide gives 
up its oxygen to the silicon, manganese, or carbon 
present, in obedience to the law of affinities ; and the 
results are silica and oxide of manganese, solids which 
appear as slag, and the gas carbon monoxide or carbon 
dioxide. The reduction of the total carbon will result 
in harder iron, and the reduction of the silicon will 
result in the appearance of all the carbon present as 
combined carbon. This result is so very decided that 
a whole heat may ^ ' run hard ' ' because of the intro- 
duction of a comparatively small amount of * * burnt 
scrap." If the effect of burnt scrap is due simply to 
the fact that the silicon has been removed by the 
oxygen of the iron oxide, then if it were melted 
together with a sufficient amount of ferro-silicon, the 
result would be gray, soft iron. But there might be 
iron oxide enough present to reduce the total carbon 
too much ; and then the silicon could not produce gray 
iron, because it would not have enough carbon to work 
with; and in this case carbon would have to be added 
as well as silicon, and pig iron high in carbon and 
silicon would serve better than ferro-silicon. The iron 
oxide which is seen as rust on the surface of scrap is 
effective in the reduction of silicon, etc., upon melting. 
Its effect is of little importance, however, as it is small 



82 MATERIALS OF MACHINES. 

in amount relatively. It must not be concluded "■'om 
this that silicon will make good iron out of all kinds of 
scrap. Some scrap is hopeless because of the presence 
of sulphur or phosphorus. It must be remembered 
that the addition of silicon to very gray iron can pro- 
duce no good result, but rather the reverse, because 
the carbon is already graphitic, and the only effect of 
the addition of silicon is its undesirable direct effect on 
the iron itself. 

Sec. 50. Mr. J. W. Keep of Detroit, Michigan, has 
made a very valuable series of experiments to deter- 
mine the influence of aluminum upon cast iron.^ He 
shows clearly that the influence of aluminum upon the 
distribution of carbon is similar to that of silicon, but 
that the effect of aluminum upon the iron itself is not 
an undesirable one, as in the case of sihcon. It would 
therefore be a better material for effecting the redistri- 
bution of carbon. It is found, however, that there are 
some very serious practical difficulties in introducing 
the aluminum, either pure or as ferro-aluminum, into 
the cast iron. 

Sec. 51. Effect of Cooling upon Cast Iron. — Cast 
iron is melted and poured into a mould. It takes the 
form of the mould, and cools gradually to the tempera- 
ture of the surrounding air. In cooling, the iron, of 
course, shrinks. The shrinkage may be divided into 
two parts: fluid shrinkage and solid shrinkage. 

* See Transactions Am. Inst. Mining Engineers, Vol. XVIII, p, 102. 



CAST IRON. 83 

After being cast the fluid iron begins to cool, and 
shrinks in volume, and the fluid iron from the 
** runners" and *' risers'' runs down to supply this 
shrinkage, until the connection between them and the 
casting is frozen up. The walls of the casting are now 
partly solidified, but are still weak, and yield to the 
force of the shrinkage of the still fluid iron inside of the 
casting, and, if it be of large volume, depressions in 
the surface result. After a little the walls become 
strong enough to resist the force, and then, since there 
is no source from which to supply the shrinkage of the 
still fluid iron at the centre of the casting, there is no 
resource but for it to become *^ spongy.'' A spongy 
cross-section is necessarily weaker than one of solid 
iron, and is therefore undesirable in a stress member 
of a machine. The fluid shrinkage may be partly 
supplied by *' feeding from a riser " in the way which 
is customary in foundries. Evidently the tendency to 
form spongy iron because of unsupplied fluid shrinkage 
will increase with the volume of the casting. After 
the whole casting has become solid, its dimensions are 
steadily reduced till it reaches the temperature of the 
surrounding air. 

Sec. 52. Experience points to the conclusion that 
castings of small cross-section shrink more than those 
of large cross-section. To test this conclusion, Mr. 
Thomas D. West made an experiment which he 
describes in his book, ^^ American Foundry Practice." 



84 MATERIALS OF MACHINES. 

He cast two bars 14 feet long, from the same iron, and 
as far as possible made the conditions of casting the 
same for both. The cross-sections were rectangular, 
one being 4" X 9'' and the other ^'' X 2'\ The total 
shrinkage for the larger bar was ^'^ and for the smaller 
one was if^\ This may possibly be explained as fol- 
lows, as Mr. West suggests: A casting cools from the 
surface, and therefore during the cooling the surface 
will be the coolest part, and the heat will increase 
toward the centre. The external portions are held 
from their normal shrinkage by the resistance of the 
hotter internal portions, which are not yet ready to 
shrink as much. This goes on till the surface has 
reached the temperature of the surrounding air and 
stops shrinking ; the hotter portions nearer the centre 
now try to shrink as they in turn cool down, but are 
prevented by the external part which has stopped 
shrinking. Whether the theory is correct or not, the 
fact remains that castings of small section shrink more 
than castings of large section. It follows that castings 
having thick and thin parts attached to each other will 
shrink unequally, and be in a state of internal stress, 
which renders them less able to withstand the action 
of external forces. 

Suppose it is required to put a strengthening rib B on 
A, Fig. 12 (^a), and that it is made of the form shown, 
i.e., thin relatively to A, and having parallel sides. 
B would shrink more than A , and shrinkage stresses 



CAST IRON, 



85 



(tension in B and compression in A) would result, 
which would be concentrated along the juncture of A 
and By and yielding would occur under a less external 
force. If the form shown in (d) were used, where the 
rib tapers from the thickness of B to the thickness of 
A, the shrinkage stresses would be distributed, and 
the casting would be stronger. 

The lessons to be learned from these facts are as 
follows: 1st. All parts of all cross-sections of castings 
for machine members should be as nearly of the same 
thickness as possible, to avoid concentrated shrinkage 




(a) 



B 




Fig. 12. 



stresses, with their accompanying weakness. 2d. If 
it is necessary to have thick and thin parts in the same 
casting, change of form from one to the other should 
be as gradual as possible. 3d. Castings should be 
made as thin as is consistent with strength, stiffness, 
and resistance to vibration, to avoid the shrinkage 
stresses, and spongy metal due to the shrinkage of 
large masses. 4th. Since some shrinkage stresses 
always must exist in cast machine members, they 
should be taken into account in designing. 

Special care should be taken in the design of wheels. 



86 MATERIALS OF MACHINES, 

because they are peculiarly liable to excessive shrink- 
age stress on account of their form. In a pulley the 
thin rim tends to shrink more than the heavier arms, 
and the rim is thereby put in tension, and the arms 
in compression. It is not uncommon to see a rim 
ruptured in this way. If the same pulley has a rela- 
tively heavy hub, the latter will remain fluid until the 
arms and rim have solidified ; the tension on the rim 
will then force the arms into the yet fluid hub, which 
in turn shrinking, will put the arms in tension. The 
arms of fly-wheels tend to shrink away from the 
heavier rim, and are therefore in tension. 

Effect of Internal Stress upon the Stress-strain 
Diagram. — Suppose that a casting be made of the 
cross-sectional form shown in Fig. 12 {a). The part 
B tends to shrink more than A , and therefore B is put 
in tension and A is put in compression. Where there 
is compressive stress and tensile force is applied, the 
first effect is the reduction of the compressive stress to 
zero. No tensile stress can be induced until the com- 
pressive stress is entirely neutralized. If a tensile 
force be applied to the casting (^), Fig. 12, it follows 
that no tensile stress will result in the part A^ and 
therefore that all the stress will be concentrated on the 
part B. To illustrate this, suppose that a tensile force 
is applied to a rope, and that half of the strands are 
tight, and the other half are slack. Stress will result 
in the strands which are tight until they are strained 



CAST IRON. 



87 



so much that the others are brought into play, and 
then the tension is sustained by the whole cross-sec- 
tion, provided the strands originally tight are not 
broken. In the casting, the part B sustains the stress 
until the compression in A is neutralized, and its tensile 
resistance is brought into play. Because of this the 
unit stress (stress per unit of cross-sectional area sus- 
taining the stress) is very great in the early part of the 
test, and the strain, having a proportionate value, is 
also much greater than it would be if the whole area 
of cross-section sustained the stress. The stress-strain 
diagram therefore takes the form shown in Fig. 13; 




Fig. 13. 

the initial part of the curve representi.ng the concentra- 
tion of stress on some fraction of the cross-sectional 
area. If the stress had been gradually relieved at A, 
the curve would have returned over AB, and OB 
would be the permanent strain or *^set. " If the in- 
ternal stress in B, Fig. 12, had been sufficiently great, 
it might have been ruptured before the tensile resist- 



SB MATERIALS OF MACHINES. 

ance o{ A could be brought into action. In any case 
the piece could not sustain as great external force as 
if there had been no internal stress, because there 
would be no time during the application of force when 
the whole area of cross-section would offer resistance 
without some part having been previously weakened. 



CHAPTER IV. 
WROUGHT IRON AND STEEL. 

Sec. 53. Influence of Certain Elements on Iron 
and Steel, Carbon. — If carbon be added to pure iron 
in increasing amount up to i .0^, the iron is changed 
first into mild steel and then into high-carbon steel. 
Accompanying this change there will be continuous 
increase in strength and hardness, and continuous 
decrease in ductility of the annealed product. After 
the percentage of carbon becomes great enough so that 
the steel will harden (say above 0.5^), the effect of 
the carbon to increase strength and hardness and to 
decrease ductility may be modified by heat treatment; 
i.e., the effect may be increased by hardening, and 
reduced to a normal value again by annealing; while 
intermediate values of strength, hardness, and ductility 
may be obtained by hardening and tempering. 

Silicon. — It is probable^ that the presence of siHcon 
up to o.Sfo has but little effect on the strength and 
ductility of steel. 

* See Manufacture and Properties of Structural Steel, by H. H. Camp- 
bell (Scientific Publishing Co.), page 257. 

89 



90 MATERIALS OF MACHINES. 

Manganese. — Up to i.o^ the effect of manganese 
upon strength, hardness, and ductility of steel is not 
very great. But when the percentage rises to 1.5^ 
the steel becomes brittle and practically useless; this 
effect continues until manganese equals about 7.0^; 
but from 7.0^ to 20.0^ manganese the steel has great 
strength, great ductility, and it is so hard that it can 
scarcely be cut at all with ordinary cutting-tools ; in 
fact, it is itself used for cutting-tools and is one of the 
so-called '^ special '' or ^* air-hardening '' steels. The 
strength and ductility of manganese steel are both 
increased by quenching from a red heat in water, 
though the hardness is thereby but little affected. 
The maximum of strength and ductility is reached at 
about 14.0^ manganese."^ This manganese steel is 
well adapted for machine parts that require great 
toughness, but it can only be used where no machine 
finishing is required. 

Sulphur. — The effect of sulphur upon steel is to 
make it red-short; i.e., to cause it to crack when 
worked at a red heat. In commercial structural steel 
the amount of sulphur is between the limits 0.02^ and 
o.iofo, and the effect of such amounts upon strength 
and ductility is unimportant. 

Phosphorus, — The effects of phosphorus upon steel 
may be summarized by saying that it tends to render 

* See Hadfield, Journal Iron and Steel Institute, Vol. II, 1888, 
page 70. 



IVROUGHT IRON AND STEEL. 9^ 

the steel unsafe when subjected to shock or any kind 
of vibratory load."^ In specifications for structural steel 
phosphorus is usually required to be less than 0.06^, 
and in some cases less than 0.03^. 

Nickel. — The effect of nickel upon steel t seems to 
be to raise the ultimate strength, and to raise the 
elastic limit in greater proportion, so that the elastic 
ratio (the elastic limit -^ the ultimate strength) is 
increased. Nickel reduces the ductility of steel, but in 
less degree than the carbon which would produce the 
same increase in ultimate strength. Hence the nickel 
steel has greater ultimate resilience than carbon steel 
of the same ultimate strength. Its elastic resilience is 
also greater because of its greater elastic range. It is 
therefore well adapted to service requiring the resisting 
of shocks, as well as to service where economy of 
weight is of great importance. 

Tungsten and Chromium. — It is found that by alloy- 
ing tungsten or chromium with high-carbon steel a 
material is obtained which is hard enough for machine- 
shop cutting-tools. The hardness does not seem to 
depend upon the carbon present, since the usual 
process of heating to redness and quenching does not 
increase it. 

There are several tungsten steels on the market, one 

* See Howe, The Metallurgy of Steel, page 67. 

f See Manufacture and Properties of Structural Steel, by H. H. Camp- 
bell (Scientific Publishing Co.), page 280. 



92 MATERIALS OF MACHINES. 

of which IS the **mushet** steel. These steels are 
forged with difficulty at a dull-red heat, and are hard 
whether they are quenched or cooled slowly. 

Recently a special steel has been brought out as a 
result of very careful investigation and experimentation 
by Messrs. Taylor and White at the works of the Bethle- 
hem Iron and Steel Company. It is called Taylor- 
White steel and contains from 0.5^ to 3.0^ of 
chromium and from i.o^ to 6.0^ of tungsten. It 
depends for its qualities not only upon its chemical 
composition, but also upon special heat treatment. 

Cutting Speed of Tools. — A limit is put upon the 
output of a cutting-tool of hardened carbon steel 
because of the limit upon the cutting speed. The 
work of removing metal is chiefly transformed into 
heat, and the temperature of the work, of the chips, 
and of the cutting-tool rises because the heat is trans- 
ferred to them. The heat is radiated away and an 
equilibrium is established between the rate of heat 
development and of heat radiation ; and as a result the 
cutting-tool acquires a definite temperature when work- 
ing conditions are established. If the cutting speed is 
increased, the work — and hence the heat developed — 
is increased proportionately, and hence the tempera- 
ture of the cutting-tool, etc., must rise in order that 
the rate of radiation shall be sufficiently increased to 
dispose of the heat developed. 

With given material to cut, and with given condi- 



IVROUGHT IRON AND STEEL 93 

tions of feed and depth of cut, there is therefore a 
correspondence between the cutting speed and the 
temperature of the cutting-tool; hence the output of 
the machine is a function of the temperature that the 
cutting-tool can endure safely. 

If the temperature of a hardened, tempered carbon- 
steel tool is raised above the temperature at which the 
temper was drawn, the temper will be further drawn, 
the tool will be softened, and the cutting edge will 
fail. 

This limits the temperature of such tools to about 
450° F. Mushet and similar steels will endure a 
higher temperature, but fail at a much lower tempera- 
ture than the Taylor- White and similar steels which 
will hold a cutting edge at a temperature of dull red- 
ness, about 1000° F. The introduction of these later 
special steels makes it possible to increase the cutting 
speed of tools on roughing-cuts from 100^ to 300^. 

Sec. 54. There may be internal stresses in forged 
material, similar to those resulting in cast material 
from unequal shrinkage. They are usually the result 
of working the material too cold. To illustrate: If a 
thin piece of ductile material be laid on an anvil and 
struck with a hammer, the piece is made thinner and 
longer and broader. Suppose now that the piece is 
thick instead of thin, and that it receives a blow as 
before: the influence of the blow extends only a little 
way into the material, and the surface is made longer 



94 MATERIALS OF MACHINES. 

and broader. Since its extension is resisted by the 
part which is uninfluenced by the blow, the material at 
the surface is put in compression, and the inner portion 
in tension. The initial part of the stress-strain diagram 
would be like that shown in Fig. 13. If the working 
be done at a red heat, the material is soft and weak, 
and therefore yields to the stresses introduced by the 
hammering or rolling, and the stresses are equalized. 

Sec. 55. Effect of Lack of Homogeneousness of 
Material on the Stress-strain Diagram. — In the 
manufacture of wrought iron the elements of the piles 
of ' ' muck-bar ' ' or scrap are drawn out in rolling into 
long lines of crystals, which are separated by more or 
less slag or oxide of iron. Since the pile may be 
made up of bars or scrap of entirely different quality, 
the structure may lack homogeneousness. This has a 
tendency to modify the form of stress-strain diagram. 
Suppose, for example, that a test-piece of wrought iron 
has half of its area of cross-section of a material whose 
elastic hmit is at E' , Fig. 14, and that the other half 
of the cross-section is of material whose elastic limit is 
at E. Let a constantly increasing tensile force be 
applied to this test-piece. When the stress reaches 
the value represented by the ordinate of E, the weaker 
part of the material begins to yield more rapidly, and 
the unit stress on the stronger part is very greatly 
increased, its elastic limit is exceeded, it also yields, 
and the curve takes the form shown, running nearly 



IVROUGHT IRON AND STEEL 



95 



parallel to the axis of X until the stress is again dis- 
tributed over the entire surface of the cross-section ; 
then the curve rises continuously until the maximum 
stress is reached. 

Steel may also show this irregularity, since different 
parts of the forging may have different elastic limit, 




Fig. 14. 



because of different heat treatment, different hot work- 
ing, or superficial cold working. 

Sec. 56. Effect of Heat Treatment on the Carbon, 
and on the Structure of Steel. — The carbon which has 
heretofore been spoken of as in combination with iron 
may exist in two forms. Hardened steel treated with 
cold, dilute hydrochloric acid is taken completely into 
solution ; whereas annealed steel leaves a carbonaceous 
residue when similarly treated. The carbon in hard- 
ened steel will be called liardening carbon, and the 
carbon in annealed steel will be called 7ton- hardening 
carbon; the temperature of the air will be called T\ 
the temperature at which red just shows in the dark 



9^ MATERIALS OF MACHINES, 

will be called V\ the temperature of full redness will 
be called W\ and the temperature corresponding to 
white heat will be called M, 

Suppose a piece of annealed steel to be gradually- 
heated from T to M, Certain changes occur in the 
carbon, and in the structure of the steel, which will 
be represented graphically. In Fig. 15, A^ C, and B 
represent carbon change, and 5, D, and F represent 
structure change. Temperature change is measured 
vertically, and change of time is measured horizontally; 
therefore an inclined line, like A^ indicates a tempera- 
ture change upward, which occupies some appreciable 
time, i.e., slow heating; while an inclined line, like 
Cy indicates a gradual temperature change downward, 
i.e., slow cooling; and a vertical line, like Ey indicates 
instantaneous cooling, or ^^ quenching." 

The size of circles of By /?, and F indicates, con- 
ventionally, the size of grain of the steel. In Ay C, 
etc., light lines indicate non-hardening carbon, and 
heavy lines indicate hardening carbon. A shows that 
as the temperature of the annealed steel is gradually 
raised, the carbon remains non-hardening carbon till 
a temperature of full redness is reached, when it all 
turns to hardening carbon. This change of carbon at 
W is an instantaneous change. B shows that the 
crystalline structure remains the same as that of the 
annealed steel (the size of which depends on previous 
heat and mechanical treatment) till IF is reached, when 



WROUGHT IRON AND STEEL 



91 







H 



O 



OOOOCXXXXXXXXXX 







9^ MATERIALS OF MACHINES, 

it becomes much reduced. This change is also instan- 
taneous, and the grain becomes as fine as is possible 
for the material. This is the structure which corre- 
sponds to the greatest ductility, toughness, and shock- 
resisting power of the material. It is therefore best 
for forged machine members. From W, with increase 
of temperature, the structure grows constantly coarser, 
and the steel more brittle and less tough, till M is 
reached. 

If this steel be cooled slowly to T, the changes 
which occur are shown by C and D. The carbon does 
not change till a temperature just above V is reached, 
when it tends to change back to non-hardening car- 
bon. This change occurs slowly, and the slow cooling 
allows it to become complete. No change of structure 
occurs during this slow cooling, but the coarse grai-n 
due to heating to M is retained. 

If the cooling from Mhad been by quenching, tke 
results would be indicated by E and F, The sudden 
cooling does not give time for the hardening carbon to 
change back to non-hardening carbon, and therefore 
the steel is hardened and the coarse grain of M is 
retained. The result, then, of slow cooling from Mis 
to produce soft, coarse, and hence brittle steel; while 
the result of quenching from M is to produce hard, 
coarse, and hence brittle steel. No method of cooling 
from M can produce fine structure. If the steel had 
been raised to any temperature between W and My the 



IVROUGHT IRON AND STEEL 99 

structure corresponding to the temperature would have 
been retained regardless of the method of cooling. If 
^either the product of CD or of EF be reheated, it re- 
tains its coarse structure till W is reached, and then 
again changes instantly to fine grain, as indicated in G, 
The steel, which was made brittle and coarse by over- 
heating, is restored by simply heating again to W, 
This restoration, however, is never perfect if the steel 
has been burnt, probably because of the iron oxide 
which has formed on the surface. 

The structure changes are a function of time, and if 
the heating in B were more gradual, a still coarser 
structure would be attained at M. In iT, if the cooling 
were effected more quickly, the structure would not 
attain the coarseness of the annealed steel. 

If a piece of annealed steel be heated to W and 
quenched, it will be exceedingly hard, and the struc- 
ture will be as fine as possible, because quenching, if 
the piece be small enough so that the cooling can be 
practically instantaneous, prevents change either of 
carbon or of structure, and both are held as they are 
at W, The material is then in the best possible con- 
dition for hardened steel. (See diagrams H and /.) 
If the piece of tool-steel be heated to W^nd allowed 
to cool slowly, the changes which take place are repre- 
sented by diagrams J^ and K. The carbon changes 
back to non-hardening carbon, and the structure 
changes back to that of the annealed steel. The 

L.nfC 



loo MATERIALS OF MACHINES. 

structure change occurs between W and F, and not 
below V. The carbon change does not begin till V is 
nearly reached, and is completed by cooling slowly 
from Fto T, 

The tendency to change hardening carbon to non- 
hardening carbon is probably strong at all temperatures 
below Vy and in the case of hardened steel it is held 
from being operative by the sudden cooling, because 
this cooling renders the materials more resistant to the 
tendency to change of carbon. If, however, a piece 
of steel which has been hardened be slowly heated, it 
is found that the tendency to change becomes operative 
at a temperature very much below V, Thus, if it be 
heated to a temperature corresponding to the forma- 
tion of straw-color oxide, there will be very perceptible 
softening of the steel. If, then, steel be heated to 
W^ and cooled by quenching to F, and then be 
allowed to cool slowly, the fine structure will be 
retained, and the hardening carbon will have had 
opportunity to change back to non-hardening carbon, 
and the material will be soft and tough. This 
method was applied with great success to the toughen- 
ing of car-axles by Mr. John Coffin at the Cambria 
Iron and Steel Works at Johnstown, Pa. 

Sec. 57. If steel be melted, and quenched from the 
fluid state, the carbon will all be hardening carbon, 
and the structure will be exceedingly fine. But if it 
be allowed to solidify, and then be cooled by quench- 



IVROUGHT IRON AND STEEL loi 

ing, the carbon will be hardening carbon, and the 
structure will be coarse. If it be allowed to solidify 
and then to cool slowly, the carbon will be non-har- 
dening carbon, and the structure will be coarse. 
These facts have been proved, and apply to the anneal- 
ing of steel castings. There has been a very general 
impression that very slow cooling of steel castings 
after solidification would result in toughening and 
softening them. The above facts, however, lead to 
the conclusion that such heat treatment would result 
in softness and brittleness, and experience proves this 
conclusion. But if they be allowed to cool to For 
below, and then be raised again to W and quickly 
cooled to Vy and then allowed to cool slowly through 
the rest of the temperature range, they will be soft, 
fine-grained, and tough. In large castings an approxi- 
mation to this heat treatment was attained by Coffin, 
by allowing the casting to cool to or below F, and 
then placing it in a reheating furnace where the tem- 
perature was raised to W. The fires were then drawn, 
the furnace-doors were opened, and the casting was 
cooled as rapidly as possible by the admission of cold 
air till V was reached, and then the furnace was 
closed, and the casting was allowed to come slowly to 
the temperature of the air. 

Sec. 58. On the Effect of Mechanical Working 
upon Structure. — If steel be heated to a white heat, 
the coarse structure corresponding to this heat may be 



I02 MATERIALS OF MACHINES. 

broken up and rendered fine by mechanical working, 
as rolling or hammering. Steel which is to be worked 
may therefore be heated above Wy and still be of fine 
grain if the working does not cease while the tempera- 
ture is yet above W, If the steel is worked at a tem- 
perature very much below W^ there is a tendency to 
introduce stress by *^cold working," as previously 
explained. Also steel is particularly brittle at what is 
usually called **blue heat" (430° to 600° F.), and if 
it be worked at this heat the brittleness remains on 
cooling. It is, however, removed by annealing. It 
is not possible to work large forgings so that there 
shall be a uniformly fine structure and no internal 
stress, because if forging ceases in any portion while 
the temperature is very much above W^ the structure 
becomes coarse, and if forging continues till the iron 
is black, internal stress is introduced; therefore this 
result should be accomplished by subsequent heat 
treatment. 

Sec. 59. Annealing. — By annealing is usually under- 
stood the process of heating to full redness, or above, 
and cooling very slowly by burying in ashes, powdered 
lime, or charcoal. The objects of annealing are: 

1st. To relieve internal stress; 

2d. To refine, i.e., to render the structure fine in 
grain ; 

3d. To change the carbon from hardening carbon 
to non-hardening carbon. 



IVROUGHT IRON AND STEEL, 103 

Internal stresses are relieved by heating to redness. 
If it is required to anneal a forging which is to become 
a machine stress member, it should be accomplished 
as follows : After forging, the piece should be allowed 
to cool to V or below; its temperature should then 
be slowly, and uniformly, raised to W\ it should then 
be quenched to F", and allowed to cool slowly in the 
air. The heating relieves any internal stresses; 
quenching from W to V fixes the fine structure, and 
confers toughness; cooling slowly from V affords 
opportunity for hardening carbon to change to non- 
hardening carbon, and therefore confers softness. The 
forging is therefore in the best condition to resist 
stress, and for working in the machine-shop. 

Sometimes annealing is required simply to confer 
softness, and the piece is to be subjected to subsequent 
heat treatment, as, for instance, the steel which is 
annealed for working into cutters, which are afterwards 
to be hardened. In this case it is only necessary to 
heat the piece to W and bury it in lime, ashes, or 
charcoal until it cools. The structure will not be the 
finest possible, but it will be refined again by harden- 
ing. 

Sec. 60. Hardening and Tempering, — Steel may be 
hardened by quenching from any temperature above 
Wy but the higher the temperature the coarser the 
structure, and the more brittle the hardened piece. If 
brittleness is objectionable, as it usually is, the harden- 



I04 MATERIALS OF MACHINES, 

ing should be accomplished by quenching from the 
lowest temperature at which hardness is conferred, i.e., 
from W, For most purposes the steel so hardened is 
still too brittle, and will not hold a thin cutting edge, 
and something of hardness is sacrificed to gain greater 
toughness, by means of the process of tempering, as 
follows: After quenching from W, the piece is slowly 
raised to a temperature at which the colored oxides 
begin to form on a polished surface of the piece. This 
softens and toughens the piece, probably by allowing 
some of the hardening carbon to change to non- 
hardening carbon. When the temperature correspond- 
ing to the required degree of softness is reached, the 
source of heat is removed, and the piece is allowed to 
cool again to the temperature of the air. 

There is a strong tendency for high-carbon steel to 
crack in hardening. This is, of course, partly due to 
the fact that all parts cannot be cooled at the same 
instant or at the same rate. Thin parts will cool more 
quickly than thick parts; external portions will be 
cooled first, and internal portions afterward. This 
will result in unequal shrinkage and severe internal 
stress, just as in the case of castings. But wrought 
iron or low-carbon steel will not crack under the same 
conditions of cooling which would cause high-carbon 
steel to crack. The reason for this is twofold: ist, 
the high-carbon steel is more brittle than the iron or 
low-carbon steel; and 2d, it has a greater coefficient 



IVROUGHT IRON AND STEEL 105 

of expansion. Therefore the effect of the unequal 
shrinkage is to produce more severe stress, and it is 
less able to withstand possible shock. It will be 
evident, therefore, that great care should be taken in 
the design of parts which are to be hardened. As in 
castings, all sections should be as nearly as possible 
of the same thickness, and all large masses should be 
avoided, as well as all sharp internal angles. As great 
surface as possible should be exposed to the action of 
the cooling medium. These precautions will insure 
an approximation to uniform cooling, and reduced 
quenching stress, and less tendency to crack. 

When a thin part is necessarily attached to a thick 
part, it is sometimes possible to fasten another piece of 
metal in contact with the thin part during heating and 
quenching. The thin part has its thickness virtually 
increased thereby, so that, if the attached piece be of 
the right dimensions, the thin part will be cooled at 
the same rate as the thick part, and quenching stress 
is thereby avoided. 

Sec. 61. Case-hardening. — A machine part of 
wrought material sometimes needs to be ductile and 
strong in order to resist stress, and at the same time 
needs to have a hard surface to resist wear. This 
result is accomplished by ' * case-hardening ' ' wrought 
iron or low-carbon steel. Pieces to be case-hardened 
are packed in an iron box, where they are surrounded 
by carbon in the form of ' ' bone-black ' ' or animal 



io6 MATERIALS' OF MACHINES. 

charcoal; the box is sealed, placed m a furnace, and 
raised to a temperature of full redness ; this tempera- 
ture is maintained from three to twenty-four hours. 
The pieces are then taken from the box and dropped 
into water while yet red-hot. During the process the 
surface of the pieces has been converted into high- 
carbon steel by the absorption of carbon, and this steel 
surface has been hardened by the quenching. The 
core or inside portion, however, remains ductile, and 
is not hardened. The surfaces of case-hardened pieces 
must be finished by grinding. Case-hardened pieces 
may be treated in exactly the same way as high-carbon 
steel: i.e., the surface may be softened by annealing; 
it may be rehardened by quenching again from W; 
and it may be tempered. The inner part is unaffected 
by this treatment, and remains ductile. 

Sec. 62. Effect of Cold Working. — When a piece of 
ductile material is strained beyond its elastic limit the 
character of the material is greatly changed. If, after 
a short interval of rest, it be tested again, its elastic 
limit and elastic resilience will be found to be higher, 
its tensile strength greater, and its ductility and ulti- 
mate resiHence less. The stiffness will be but slightly 
changed, if at all. By cold working, i.e., by any 
means that gives permanent set to cold material, the 
elastic range is increased, the piece is made stronger 
and better able to resist shocks within the elastic limit, 
but less ductile, and less able to resist shocks exceed- 



IVROUGHT IRON AND STEEL 107 

ing the elastic limit. These changes are shown 
graphically in Fig. 16. The stress-strain diagram 
OEABCD is such as would usually result from a test 
of a ductile material, like mild steel or wrought iron. 
On reaching some point, as E^^ stress is gradually 
relieved, and the curve descends to the X-axis at 0^, 
On reapplication of tensile force the curve rises along 
the line O^E^ nearly parallel to OE, The elastic limit 
is now at jEp a point much higher than the original 
elastic limit E, The curve then continues, a little 
higher than it would if the stress had not been discon- 
tinued, until the maximum is reached at H.'^ 

If the force could have been instantly reapplied at 
0^ , the line GHJ would probably have coincided with 
ABC, because the change is a function of the time of 
resting, after relief of stress. OEABCD may be con- 
sidered the stress-strain diagram of one material, and 
O^E^GHJth.^ stress-strain diagram of another material. 
It is as if a new test began at O^ . Let a represent the 
first diagram, and d the second. The elastic range of 
dy represented by O^E^y is greater than that of a, 
represented by OE, The elastic resilience of ^, repre- 
sented by the area O^E^F^ , is greater than that of a, 

^ That the maximum strength is increased has been demonstrated by 
Bauschinger. He first broke a long test-piece by tensile force. It was of 
uniform cross-section, and hence all of its parts must have been strained 
well past the elastic limit. He then broke one of the pieces and found 
increased strength. This was repeated six times, and each repetition 
resulted in increased strength. 



io8 



MATERIALS OF MACHINES. 



IVROUGHT IRON AND STEEL 109 

represented by OEF. Experiment has proved that 
the points B and C are not changed in their relation to 
the axis of Y by the relief of stress ; and therefore the 
ductility of ^, represented by OD, is greater than the 
ductility of by represented by OJ), The ultimate 
resilience, proportional to the total area under the 
stress-strain curve, is evidently greater in a than in b. 
O^E^ is nearly parallel to OEy and hence rigidity is 
nearly the same for both. 

If, instead of the almost immediate reapplication of 
force, a considerable interval of rest had been allowed, 
say twenty-four hours, the elastic limit and ultimate 
strength would have been still further raised, and the 
diagram would be like O^E^LMN. If stress were not 
discontinued till the maximum had been nearly 
reached, the strained material would resemble a very 
brittle material. 

It may be stated as a conclusion warranted by ex- 
periment (see Trans. Am. Soc. Civil Engineers, Vol. 
XXIV, p. 159) that stress of any character which 
strains a ductile material beyond its elastic limit will 
render it stronger, and less ductile in resisting stress of 
any other character. Annealing removes these effects 
almost completely. The process of **cold rolling,** 
by which shafting is produced, illustrates the altera- 
tions of the qualities of ductile material due to straining 
beyond the elastic limit. In this process iron is passed 
cold through highly finished rolls, under intense pres- 



no MATERIALS OF MACHINES, 

sure. The rolled piece has its length increased and 
its cross-section reduced, and therefore, since the 
material takes a **set," it must be strained by the 
treatment past its elastic limit. 

Professor Thurston made a series of tests to deter- 
mine the effect of cold rolling upon iron. His experi- 
ments show that there results from the process (^) an 
increase in tensile strength of from 25^ to 40^; (^) an 
elevation of the elastic limit of from 80^ to 125^; {c) an 
increase of elastic resilience of from 300^ to 400^; (d) 
a decrease in ductility of about 75^; and (e) a decrease 
of ultimate resilience of about 40^. If, therefore, the 
product of the process is required to withstand stress 
(and especially shock), which cannot exceed the elastic 
limit, it is far better than the untreated iron; but if 
there is a possibility of shock exceeding the elastic 
limit, the unrolled iron might be better. 

The process of ' ^ wire-drawing, " i.e., reducing the 
size of wire with increased length by drawing cold 
through dies, produces the same result as cold rolling; 
the wire requiring frequent annealing to restore duc- 
tility. 

Sec. 63. The Effect of Repeated Stress. — Between 
the years 1859 and 1870 A. Wohler planned and 
executed a series of experiments for the Prussian 
Government to determine the laws governing the 
behavior of metals under repeated stress. By means 
of his machines, forces of known value producing ten- 



IVROUGHT IRON AND STEEL m 

sile, compressive, torsional, or transverse stress could 
be applied with indefinite repetition, until rupture oc- 
curred, or until it was considered proved that indefinite 
repetition of stress could not produce rupture. He 
formulated a law from the experimental work, which 
in substance is as follows: Material may be broken by 
repeated application of a force which would fail to pro- 
duce rupture by a single application. The breaking is 
a function of range of stress; and as the recurring 
stress increases y the range necessary to produce rupture 
decreases. If the stress be reversed^ the range equals 
the sum of positive and negative stress. 

The experimental work of Wohler has been amplified 
and supplemented by the very careful work of Professor 
Bauschinger of Munich. He draws the following con- 
clusions from his experimental work: 

a, *^With repeated tensile stresses, whose lower 
limit was zero, and whose upper limit was near the 
original elastic limit, rupture did not occur with from 
5 to 1 6 million repetitions.'* He cautions the designer 
that this will not hold for defective material, i.e., a 
factor of safety must still be used for this reason ; and 
that the elastic limit of the material must be carefully 
determined, because it may have been artificially raised 
by cold working, in which case it does not accurately 
represent the material. This original elastic limit may 
be determined by testing a piece of the material after 
careful annealing. 



IT2 MATERIALS OF MACHINES, 

b, ** With often repeated stresses, varying between 
zero and an upper stress, which is in the neighborhood 
of or above the original elastic limit, the latter is raised 
even above, often far above, the upper limit of stress, 
and it is raised higher as the number of repetitions of 
stress increases, without, however, a known limiting 
value, Ly being exceeded." 

c. ''Repeated stresses, between zero and an upper 
limit below Z, do not cause rupture ; but if the upper 
limit is above Z, rupture will occur after a limited 
number of repetitions. ' ' 

b may be explained more fully. Suppose that a 
piece whose elastic limit is 28,000 pounds per square 
inch is subjected to repeated stress, whose limits are o 
and 29,000 pounds per square inch. Since the elastic 
limit is exceeded, permanent set results; i.e., the piece 
is '* cold-worked.'^ But the cold working raises the 
elastic limit, and each repetition of stress raises it more. 
The elastic limit passes 29,000 pounds per square inch, 
and the conditions are those of a material subjected to 
repeated stress within the elastic limit, and rupture 
will not result. But the elastic limit cannot be raised 
beyond a certain limiting value, L, If (see c) the 
limits of repeated stress are o, and some value, T, 
above Z, then repetition of 7" cannot raise the elastic 
limit above its own value, and the conditions are those 
of a material repeatedly strained beyond its elastic 



IVROUGHT IRON AND STEEL 113 

limit, and the experiments show that the piece will 
ultimately be broken. 

From this it follows that keeping within the original 
elastic limit insures safety against rupture from repeated 
stress, if the stress is not reversed; and that when the 
stress is reversed the total range should not exceed the 
original elastic range of the material. 

Sec. 64. Factors of Safety. — If repeated stress were 
the only possible cause for failure, it would only be 
necessary for the designer to keep the range of stress 
a little less than the original elastic limit of the 
material. But failure of a machine stress member may 
result not only from 

{a) Repeated stress, but also from 

{b) Flaws, or other imperfections in the material; 

{c) Internal stresses; 

(</) Unhomogeneous material; 

(e) Shocks ; 

(/") Stresses which cannot be estimated. 

To cover all these a factor of safety is used; i.e., 
the working unit stress is equal to the ultimate unit 
strength of the material, divided by a number which is 
called the factor of safety. 

Materials are so various in their qualities, and the 
conditions to which they are subjected as machine 
stress members are so different, that it is impossible to 
give any value for a factor of safety to cover all cases. 

For ductile resilient material, like mild steel used in 



114 MATERIALS OF MACHINES. 

building-frames, roof-trusses, bridges, etc., a lowvalue 
may be used for the factor of safety, because by r, and 
d above may be practically eliminated by proper 
specifications and careful inspection, and because the 
loads are known. 

But in machines the conditions are dynamic, and it 
is more difficult to estimate stresses ; especially when 
accidental increases of velocity are possible, or when 
lost motion, due to wear or imperfect adjustment, 
enable moving parts to deliver blows to other parts. 

For unresilient or brittle materials, like cast iron, 
the factor of safety needs to be larger; not only 
because of less shock-resisting capacity, but because 
shrinkage stresses are always present, and there is, in 
many cases, danger of blow-holes or spongy sections. 
The weakening effect of these varies with the size and 
form of the member, and with the conditions of casting. 
Hence the factor of safety must be determined in each 
case by the judgment of the designer. 



CHAPTER V. 
ALLOYS. 

Sec. 65. It has been explained that iron unites with 
the substances carbon, manganese, sihcon, sulphur, 
phosphorus, chromium, tungsten, aluminum, and 
nickel; and that the resulting mixtures have certain 
physical qualities due to the union. These are alloys^ 
although not usually called so. It is found that nearly 
all of the metals used by the engineer will unite with 
each other in certain proportions, many of them in all 
proportions, and that the alloys so produced have 
physical qualities which differ from those of either of 
their constituents. 

The subject of the constitution of alloys is being in- 
vestigated very exhaustively with the aid of microscopic 
examination. A discussion of this very interesting 
subject is beyond the scope of this work, and the 
student is referred to Vols. I and II of **The Metal- 
lographist, ' ' edited by Albert Sauveur, published by 
the Boston Testing Laboratories, 446 Tremont St., 
Boston, Mass. 

Sec. 66, The alloys of greatest importance to the 
engineer are the copper alloys, i.e., the combinations 

115 



ii6 MATERIALS OF MACHINES. 

of copper with some one or more other metals, in 
varying proportions. 

Alloys oi copper and tin are usually called Bronze. 

Alloys of copper and zinc are usually called Brass. 

Alloys of coppery tin, and zinc have been named by 
Dr. Thurston Kalchoids. 

Bronze. — If successively increasing amounts of tin 
be added to pure copper, it is found that certain 
changes occur in color, strength, and ductility. The 
changes in strength and ductility may be represented 
graphically. The curves in Fig. 17 are plotted from 
the very complete experiments of Dr. Thurston (see 
** Text-book of the Materials of Construction,*' page 
451). From these curves it appears that as the 
amount of tin is increased, the strength increases until 
tin 18^, copper 82^^ is reached; from this point to tin 
30^, copper 70^, the strength falls off very rapidly; 
and the alloy remains weak through the rest of the 
range. The ductility rises from tin o, copper 100, to 
tin 4, copper 96, and then falls to zero at tin 22, 
copper 78. The ductihty rises again near the tin end 
of the range to a very high value. The curves show 
that the only part of the range where strength and 
ductility are both high, and where resilience is there- 
fore also high, is between tin 10, copper 90, and tin 
o, copper 100. In practice *' gun-bronze '' is practi- 
cally the only bronze used for machine parts. Its 
composition varies but little from tin 10, copper 90. 



ALLOYS. 



117 




Ii8 MATERIALS OF MACHINES. 

The increasing strength resulting from increased 
proportion of tin is accompanied by increasing hard- 
ness and decreased coefficient of friction; i.e., it has 
become a better material for journal-bearings. The 
alloy from copper 70 to copper 10 is evidently a very 
brittle material. But from copper 10 to copper o the 
high ductility and low strength show a resilient, weak 
material. The coefficient of friction is, however, less 
even than that of the alloys at the other end of the 
range, and it is therefore a good material for journal- 
bearings and slides ; but it is so weak that it has to 
be enclosed in shells of stronger material; i.e., it is 
used as a lining for brass or cast-iron journal-boxes. 
A small amount of antimony added to this gives the 
alloy known as Babbitt metal. Tin 33, copper 6y^ 
gives an alloy which, while it is evidently exceedingly 
brittle, yet it is susceptible of a very high polish, and 
is used for the metallic mirrors in certain optical instru- 
ments. It is called ^'speculum-metal.'' Tin 23, 
copper 'jj is a strong alloy, lacking in ductility, which, 
because of its sonorousness, is used for bells. It is 
called '^ bell-metal." 

In proceeding from the copper to the tin end of the 
range the color changes, first, from the color of pure 
copper to a yellow at copper 80, turning to gray at 
copper 70, and changing gradually to tin color during 
progress toward copper o. 

Sec. 6y, Brass. — Fig. 17 also shows curves of 



ALLOYS. 119 

strength and ductility of the brasses or copper-zinc 
alloys. These are also drawn from the results of 
Dr. Thurston's experiments (see ** Text-book of the 
Materials of Construction," page 461). Inspection of 
these curves shows that the copper-zinc mixture offers 
a much wider range of alloys useful to the engineer 
than the copper-tin mixture; the range, both of high 
strength and high ductility, being much greater in the 
former. The addition of zinc to copper has an effect 
similar to that of the addition of tin to copper. The 
maximum effect is greater in the case of zinc, but it 
requires a greater percentage of the zinc to produce it. 
The color changes are similar to those in the copper- 
tin mixture. There is no return of ductility at the zinc 
end of the range, and hence the white alloys of copper 
and zinc are seldom used. The curves may be used 
to indicate proportions in mixing bronzes or brasses 
for any special duty requiring strength, ductility, and 
resilience. 

Sec. 68. Kalchoids. — Dr. Thurston made a very 
full and careful series of experiments on the kalchoids, 
or ternary alloys of copper, tin, and zinc. He repre- 
sented the whole field of possible combinations of the 
three metals by an equilateral triangular area. Many 
points at equal distances from each other were located 
in this area, and each represented an alloy with certain 
proportions of the three constituents. Alloys were 
made corresponding to each point, and tested. At 



120 MATERIALS OF MACHINES. 

each point was erected a piece of wire whose height 
represented the strength of the alloy represented by 
the point. Plastic material was then filled in between 
the wires, and its surface was moulded so that the 
points of the wire just showed through. This surface 
represented topographically the varying strength of all 
possible mixtures of copper, tin, and zinc, and the 
alloy of maximum strength was thereby located. (See 
Thurston's *^ Text-book of the Materials of Construc- 
tion,'* page 466.) 

Sec. 69. Two other alloys of copper require atten- 
tion : phosphor bronze and manganese bronze, 

Phosphor Bronze, — When any alloy containing a 
high percentage of copper is melted in contact with 
the air, there is a strong tendency to form copper 
oxide, the affinity of copper for oxygen being exceed- 
ingly strong. If the alloy cools mixed with copper 
oxide, it is weak and brittle, just as iron containing 
iron oxide is weak and brittle. Copper alloys are 
usually melted with charcoal upon the surface to pre- 
vent oxidation, but the prevention is not complete. If 
phosphorus be added to the alloy just before pouring, 
the copper oxide is reduced and phosphoric acid is 
formed, i.e., the alloy is purified by the fluxing action 
of the phosphorus. This increases both the strength 
and ductility of the alloy. If an excess of phosphorus 
be added, part of it may combine with the alloy and 
increase its strength and ductility; but it is probable 



ALLOYS. 121 

that the chief value of its presence is to prevent the 
formation of oxide of copper during remelting. 

Manganese Bronze is made either by fusing together 
{a) copper and black oxide of manganese, or {b) 
copper or bronze and ferro-manganese. In the first 
case the product is an alloy of copper and manganese, 
and in the second an alloy of copper, manganese, and 
iron, or copper, tin, manganese, and iron. Some of 
the manganese is effective in removing, or preventing 
the formation of, oxide of copper, while the remainder 
combines with the copper or bronze to give it very 
greatly increased strength, ductility, and toughness. 
A manganese bronze, copper 83.45^, manganese 
13.48^, iron 1.24^, has a strength and ductility equal 
to that of open-hearth steel with 0.2^ carbon. It is 
much used for marine propeller-wheels because it does 
not corrode easily. 

All of the useful copper alloys are more or less 
forgeable. **Muntz metal," copper 60, zinc 40, is 
rolled at a red heat into plates for sheathing ships, and 
into forms for bolts and other fastenings. It is 
stronger, cheaper, and more durable than pure copper. 
The effect of cold working upon the copper alloys is 
similar to that upon iron and steel; viz., the strength 
and hardness are increased and the ductility is 
decreased, and hence the material is more brittle. 
This will be clear on comparing hard-drawn brass wire 
with the same wire after annealing. 



CHAPTER VI. 

SELECTION OF MATERIAL. 

Sec. 70. The more important materials used in 
machine construction may be brought together in a 
table as follows: 

1. High-carbon Steel. 

2. Mild Steel, produced by the Bessemer or open- 
hearth process. 

3. Wrought Iron. 

4. Cast Iron. 

5. Malleableized Cast Iron, or Malleable Iron. 

6. Steel Castings. 

7. Brass or Bronze. 

8. White Metal. This name includes all of the 
white alloys used for lining journal-boxes, etc. 

The qualities upon which selection chiefly depends 
are indicated in the table on page 123 

Sec. 71. The fitness of materials for wearing surfaces 
also needs consideration. 

The surfaces of machine parts that move over each 
other under pressure are normally separated by a film 
of lubricating material. But under exceptional condi- 
tions the metallic surfaces themselves may come into 

122 



SELECTION OF MATERIAL. 



123 



contact; when this occurs the danger of roughening or 
destroying the surfaces depends somewhat upon the 
excellence of the surface and kind of material. 



Material. 


Tensile 
Strength. 


Compressive 
Strength. 


Resilience or 

Shock 

Resistance. 


Shaped for 
Use by 


I 
2 

3 

4 

7 
8 


very high 

high 
medium 

low 
medium 

high 

low 
very low 


very high 

high 

medium 

very high 

high 


medium 
high 
high 
low 
high 
high 

medium 


forging 
forging 
forging 
casting 
casting 
casting 
j casting or 
( forging 
casting 



A material may be well adapted for wearing surfaces 
because of {a) hardness, [a) slipperiness, {c) homo- 
geneousness, or {d) because it is partly composed of 
lubricating material. 

Thus, {a) hardened tool-steel is difficult to roughen 
because of its hardness; {b) white metal, though soft, 
is difficult to roughen, because the roughening agent 
slides over the slippery surface; {c) mild steel would 
have less tendency to roughen an engaging surface 
than wrought iron, because the former has a homo- 
geneous surface, while the latter carries streaks of 
gritty cinder ; [d) cast iron tends to wear smooth rather 
than rough, because it contains graphitic carbon, a 
lubricating material. 

The ideal for rotating surfaces would be a hardened, 
accurately ground, crucible-steel journal, with itg 



124 MATERIALS OF MACHINES. 

bearing lined with white metal. But here the question 
of cost enters, for the cost of the journal specified 
includes high first cost for the crucible steel, the cost 
for hardening, and a cost incident upon the loss of 
expensive parts through cracking in the process of 
hardening. In addition to this, an expensive plant is 
required for the hardening of large journals. 

In standard practice mild-steel journals are used 
with bearings lined with w^hite metal; but there are 
often conditions that lead to the use of other materials. 

Sliding surfaces in machines are often formed upon 
cast-iron members, and the engaging surface is also of 
cast iron. The frictional loss may be reduced by giv- 
ing one surface a white-metal covering. 

Sec. 72. To illustrate the selection of materials for 
machine parts, a few typical examples will be dis- 
cussed. 

The cylinder of a steam-engine, with its ports and 
its connected steam-chest, is of such complicated form 
that it would be almost impossible to shape it by forg- 
ing ; or if the forging were possible, it would be too 
expensive. The possible materials which may be used 
for such a cylinder are, therefore, only those which are 
shaped by casting. Brass and bronze would have no 
advantage over cast iron, and would cost about ten 
times as much. They are, therefore, out of the ques- 
tion. Steel casting might be used, but the first cost of 
the material would be som.ewhat greater, and the cost 



SELECTION OF MATERIAL I25 

of working in the machine-shop would be very much 
greater. Additional strength and resilience would be 
gained, but this is unnecessary, as cylinders, even for 
very high pressures, can be made of cast iron, amply 
strong and resilient, and yet not objectionably thick. 
Moreover, cast iron is one of the very best possible 
materials for the wearing surfaces of the cylinder and 
valve -seat. Cylinders subjected to excessively high 
pressure, as 300 to 700 pounds per square inch, should 
perhaps be made of steel castings ; as, for instance, the 
cylinders of pumps for pipe-lines, or for supplying 
hydraulic machinery. 

The piston-rod of a steam-engine is of mild steel. 
The entire force of the steam acting on the piston must 
be transmitted to the cross-head through the piston- 
rod ; also, since the effective area of the piston on the 
crank side equals the total area of the piston less the 
area of the rod, and since the effective area needs to 
be as large as possible, the rod should be as small as 
possible. There is always the liability to shocks, and 
therefore, since the rod must be small and at the same 
time strong, and must also be capable of resisting 
shocks, a material is required of high unit strength and 
of high resilience. Soft steel is the material which 
combines these qualities. 

A steam-engine cross-head pin is always made 
much larger than is necessary to safely resist shearing, 
or springing by flexure, to insure the maintenance of 



126 MATERIALS OF MACHINES, 

lubrication ; cast iron might serve, then, as far as 
strength and stiffness are concerned, and in fact is 
sometimes used. But there is another important con- 
sideration : because of the vibratory motion of the con- 
necting-rod on the pin, there is a tendency to wear the 
pin oval, and when the boxes are ** keyed up,** they 
will bind when the rod is in its position of greatest 
angularity, if it is properly adjusted when the rod is on 
the centre line of the engine. Because of this it is 
desirable to reduce the wear to a minimum, and this 
points to the selection of a hard material. Hardened 
tool-steel might be used, but it is more expensive than 
soft steel or wrought iron, and there is the danger of 
hidden cracks, resulting from the hardening, which 
may cause accident. If soft steel be case-hardened, it 
will combine a hard surface to resist wear, with a soft 
resihent core, free from the danger of cracks. Wrought 
iron case-hardened might be used, but wrought iron, 
because of the method of manufacture, has streaks of 
cinder in its surface, and lacks the homogeneity of the 
steel, and is therefore harder to make, and to keep 
truly cylindrical. It therefore should not be used 
where perfection of bearing and accuracy of movement 
are essential. 

The connecting-rod of a steam-engine is subjected 
to the alternate tension and compression resulting from 
the pressure on the piston, and also to a flexure stress 
due to its vibratory motion. These stresses are very 



SELECTION OF MATERIAL 127 

severe, and there is also liability to shock. The 
material of the rod should be strong and resilient, and 
soft steel would naturally be selected, since it is a 
forgeable material. But there is another important 
consideration. The rod is to be finished, and wrought 
iron is much more cheaply worked in the machine-shop 
than soft steel, and the expense of forging is also much 
less. The lack of homogeneity is of no importance, 
as no part of the rod is a bearing-surface. Many con- 
necting-rods are made of steel casting, and finished by 
painting. This makes a cheaper rod, but there is 
always the danger of hidden defects, like cracks, due 
to the excessive shrinkage, or ** blow-holes,** which 
may weaken the rod enough to cause accident. 

Sec. 73. The cross-head of a steam-engine is com- 
posed of two parts: (^) that which serves to transmit 
the pressure from the piston-rod to the cross-head pin, 
and {b) that which engages with the guide to produce 
rectilinear motion. The stresses on (^) are severe, 
and there is liability to severe shock; hence it must be 
of strong resilient material; the stresses on {p), how- 
ever, are less, but it must be of material which will run 
well with the guide, which is usually of cast iron, 
being a part of the engine-bed. The cross-head may 
be made of materials as follows: {a) may be made of 
forged wrought iron or soft steel, and (J?) may be of 
cast iron bolted to (<2), or the whole cross-head may 
be made of cast iron, the part {a) being made enough 



128 MATERIALS OF MACHINES. 

larger than before to be sufficiently strong; or the 
cross-head may be made a casting of steel and a 
* ' shoe " or * ' gib ' ' of cast iron or brass may be added 
to provide a proper surface to run in contact with the 



guide. 



The crank-pin of a steam-engine is subjected to the 
same stress as the cross-head pin, and the velocity of 
rubbing surface is very much greater, hence the ten- 
dency to wear is greater. But the tendency to wear 
* * out of round ' ' is less and therefore there is less 
interference with the correct adjustment of the boxes; 
hence there is less reason for keeping the wear a mini- 
mum; a good journal surface is necessary, and soft 
steel is used without case-hardening. 

The main shaft of a steam-engine needs to be 
strong and rigid to resist a combination of severe 
stresses, i.e., the torsional and transverse stress from 
the connecting-rod, and the transverse stress due to 
the weight of the fly-wheel, and the belt tension. It 
must also afford a good journal surface, and for these 
reasons it is made of soft steel. 

The function of the fly-wheel of a steam-engine is 
to adapt a varying effort to a constant resistance, and 
it does this by absorbing and giving out energy 
periodically by virtue of its inertia, which is propor- 
tional to its weight; it therefore needs, above all 
things, to be heavy; it also needs to be able to resist 
the bursting tendency of the centrifugal force due to 



SELECTION OF MATERIAL 129 

its rotation. The most suitable material is therefore 
that which gives the greatest weight in the required 
form, with the required strength, for the least money; 
and cast iron best fulfils these requirements. 

An engine bed or frame, when it is in one piece, is 
of cast iron, and the reasons are obvious: its form is 
complex, and could only be produced by casting; 
weight is not objectionable, but rather an advantage, 
since it absorbs vibrations ; cast iron is amply strong, 
and affords good wearing surfaces for the cross-head 
guides. Wrought iron is used for engine-beds where 
vibrations are less important, as in the locomotive, and 
where lightness and compactness are very desirable, 
as in some marine engines. The beds of some large 
roll-train and blowing engines are built up of wrought 
and cast iron. 

The journal-bearings, or boxes for the cross-head 
pin, the crank-pin, and the journals of the main shaft 
are usually made now of cast iron or brass, with a 
Babbitt-m.etal lining, because, first, good Babbitt 
metal (tin 80, copper 10, antimony 10) is found to be 
a better bearing metal than brass, i.e., it runs with less 
tendency to heat; and second, in the case of the 
cutting out of the surface, the Babbitt-lined box is far 
more quickly and cheaply renewed than the solid brass 
box. 

The eccentric and its strap are almost invariably 
made of cast iron, because they are forms which are 



130 MATERIALS OF MACHINES. 

forged with difficulty, and the cast iron affords ample 
strength and excellent wearing surfaces. The eccen- 
tric-rod, on the other hand, would be cumbersome and 
ugly in appearance if it were made of cast iron and 
given sufficient strength. It is a form which may be 
easily either forged or cast, and is made of forged 
wrought iron or steel, or of cast steel, or of malleable- 
ized cast iron. Rocker-arms also, when they are used, 
require to be of a resilient material, and when of simple 
form may be forged of wrought iron or steel, and 
when of more complex form may be of malleableized 
cast iron, or steel casting. The valve is usually of 
somewhat complex form, and needs to wear well with 
the cast-iron valve-seat, and is almost invariably of 
cast iron. 

Sec. 74. Considerations similar to those above apply 
to the selection of proper material for the parts of 
machine tools. Thus, in the case of a lathe, the bed, 
legs, head, and tail-stock, cone, gears, etc., are of cast 
iron, because they are all forms which are most cheaply 
and satisfactorily produced by casting, and the cast 
iron affords the required strength and stiffness, and 
satisfactory wearing surface, where they are required. 
Such parts as lead-screws, feed-rods, and other parts 
which are subjected to some considerable stress, and 
have great length relatively to their lateral dimensions, 
are made necessarily of wrought iron or steel. Many 
of these parts may be finished in the machine-shop 



SELECTION OF MATERIAL 131 

directly from merchant-bar stock, thus saving expense 
for forging. 

The material for the parts of planing-, milling-, and 
drilling-machines are determined from exactly similar 
considerations. 

Spindles, however, require special attention. In 
lathes, milling- and grinding-machines the accuracy 
of the work produced depends largely upon the 
accuracy of the spindle. 

The vital point is therefore to maintain this accuracy, 
i.e., to prevent wear as far as possible. It would seem 
then that hardened tool-steel would be the best 
material. But since only a very small amount of stock 
can be removed by the grinding-machine after the 
piece is hardened, the spindle must be roughed out 
very nearly to size before it is hardened ; this involves 
a very considerable expense, and there is danger that 
it may crack in hardening, or spring so as not to hold 
up to finish, in which case the loss is great, and it is 
found that the risk cannot be taken. The next best 
thing is to specify machinery steel high in carbon (say 
0.4^), and to use this harder material for the spindle 
without hardening. In milling-machines and in some 
lathes the main spindle-box is solid, of tool-steel, 
hardened and ground (the risk of loss being less in this 
case), and the spindle as before is of 0.4^ carbon 
machinery-steel. The wear is thus greatly reduced, 
and the possibility of wear after long use is provided 



132 MATERIALS OF MACHINES, 

against by making the bearing taper, and providing 
end adjustment. The spindles of very large lathes are 
made of cast iron, because forged material would be 
too expensive. The wear is reduced by making the 
journals very large. 

Sec. 75. In the steam or hydraulic riveter the 
main frame which supports the cylinder, and carries 
the guide for the moving die, may be of any reason- 
able size, and therefore can be made strong enough to 
resist even the very great forces applied to it, if the 
material used is cast iron. But the *^ stake,'* the 
member which carries the stationary die, must resist 
exactly the same forces as the main frame, and must 
also be small enough so that small boiler-shells, and 
even flues, can be lowered over it to be riveted. The 
*< stake ** is therefore of forged wrought iron or steel, 
or else a steel casting. 

Sec. y6. Suppose that in a machine there is need of 
a gear and pinion whose velocity ratio is 8 to i , and 
that the force transmitted is large. A tooth of the 
pinion comes into action eight times as often as a tooth 
of the gear, and therefore would wear out in one eighth 
of the time if both were of the same material; then, 
too, the form of the pinion-tooth in most systems of 
gearing is such that it is much weaker than the gear- 
tooth. The material for the pinion needs, therefore, 
not only to be stronger, but also better able to resist 
wear. The gear is made of cast iron ; if the teeth are 



SELECTION OF MATERIAL. I33 

cut, the pinion may be made of forged steel; if the 
teeth are cast and used without ''tooling/' the pinion 
may be made a steel casting. 

Sec. 77. Material for Springs. — Springs are useful 
as machine parts because of their capacity for yielding 
without taking permanent set. The yielding, there- 
fore, must occur with stresses that do not exceed the 
elastic limit. Clearly, then, the material with large 
elastic range, i.e., with high elastic limit, is the best 
material for spring machine-members. 

Crucible-steel has the highest normal elastic limit, 
and this limit is raised by hardening and tempering. 
This is the most commonly used material. Untreated 
mild steel may also be used, but with given stress the 
spring must have greater weight than if higher carbon 
steel were used. The steel may have its normal 
elastic limit artificially raised by cold working (cold 
rolling or wire-drawing), and this improves it as a 
spring material. Brass, bronze, and other alloys are 
used for springs, but usually in the form of hard-drawn 
wire with an artificial elastic limit. 



INDEX, 



PAGE 

Acid Bessemer blow, graphical representation of 53 

* • lining 20 

Alloys 115 

Aluminum, effect of, upon cast iron 82 

Annealing , 102 

Basic Bessemer blow, graphical representation of. 50 

•' *• process 46 

* ' lining 20 

Bauschinger, work of, on repeated stress ill 

Bed of engine, material for 129 

Bessemer process 43 

Blast-furnace 23 

<* <* , chemical changes in 26 

Blister-steel 42 

Bloom 39 

Bog ores 20 

Brass 118 

< ' diagram of qualities 117 

Breaking strength 59 

British thermal unit 3 

Bronze 116 

'^ diagram of qualities 117 

Burnt scrap 80 

135 



n 



<( 



136 INDEX. 

PAGE 

Calcining 21 

Calorific intensity 4 

' * of carbon, determination of 4 

' * ' ' carbonic oxide, determination of. 6 

" '* hydrogen, determination of 7 

Calorific power 3 

< < powers, table of. 4 

Capacity, increase of, due to hot blast in blast-furnace 30 

Carbonate, ferrous 20 

Carbon, distribution of, in cast iron 69 

*' , '* a ^ a a a as affected by silicon, manganese, 

etc 73 

Carbon, effect of redistribution of, in cast iron 70 

*' , " *' heat- treatment upon, in steel 95 

* * , hardening 95 

'' in basic Bessemer process 46 

' ' , influence upon steel 89 

' ' , introduction of, in blast-furnace 26 

'* , non-hardening 95 

*^ , removal of, in Bessemer process 4§ 

Case-hardening 105 

Castings, design of 85 

<< , dilution of carbon in, by melting with steel scrap 78 

* ' , use of scrap in melting 79 

Cast iron, carbon in 68 

changes in, due to remelting 79 

, composition of 67 

, effect of cooling upon 82 

' ' aluminum upon 82 

, grades of 69 

** '' mixtures, diagram showing 75 

'* ** , produced in foundry 32 

Cementation process 41 

Charcoal. 1 1 

Chilling of iron castings 73 

Chromium, influence upon steel 91 

Coal..... 9 

Coke 10 

<* , descent of, in blast-furnace 29 



5 



1 



INDEX. 137 

PAGE 

Cold working, effect of, upon steel 106 

Combustion, complete 3 

Connecting-rod, material for 126 

Converter, Bessemer 43 

Cooling, effect of, upon cast iron 82 

Crack, tendency of steel to, in hardening 104 

Crank-pin, material for 128 

Cross-head, '' '' 127 

* ' < * pin, material for 125 

C rucible process 42 

Cupola furnace , 33 

Cutting speed of tools 92 

Cylinder of steam-engine, material for 124 

Direct methods, chemical reactions in 22 

< ' ' * for production of iron 22 

Dolomite 20 

Dry-puddling 38 

Ductile castings 54 

Ductility 52 

Early methods, iron production 22 

Eccentric, material for 129 

Eccentric-rod, material for 130 

'<• -strap, *' ** 129 

Elasticity 59-62 

Elastic limit 59 

59 



* ' strain . 



Factors of safety 113 

Ferric oxide 20 

*' " hydrated 20 

Ferro-manganese 46 

Ferrous carbonate 20 

Fettling ^7 

Fire-clay 19 

Flame, oxidizing, neutral or reducing 36 

Flux 23 

Fly-wheel, material for 128 



138 INDEX. 

PACK 

Foundry 32 

Frame of engine, material for 129 

Fuel, economy of, in blast-furnace due to hot blast 30 

** , gas 12 

Fuels, artificial 10 

<' , classification of g 

** , preliminary consideration of 2 

'^ , raw 9 

Furnace, cupola 33 

Canister 19 

Gas-current, ascent of, in blast-furnace 30 

Gas-fuel 12 

* * * ' , production of. 13 

Gas-producer 15 

Hsematite, brown 20 

'' , red 20 

Hardening of steel 103 

Heat treatment, effect of, on structure of steel 95 

'< '^ , '* ", '^ the carbon of steel 95 

Heat unit 3 

Homogeneousness, lack of, effect on stress-strain diagram 94 

Hooke's law 59 

Hot-blast for blast-fiirnace 30 

Illuminating-gas process 13 

Iron, sources 20 

Journal bearings, material for 129 

Kalchoids 119 

Limonite 20 

Machine-tool parts, material for 130 

Magnesian limestone 20 

Magnetic oxide 20 

Magnetite 20 



INDEX. 139 

PAGE 

Malleable castings 55 

** ** analysis of 55 

Manganese bronze 121 

* ' , influence upon steel 90 

* * , introduction of, into cast iron 27 

** , removal of, in Bessemer process 45 

'' , '' *',•' puddling '' 38 

Materials, general qualities of. 123 

Merchant-bar 39 

Metallurgy of iron and steel graphically represented 37 

Muck-bar 39 

Muntz-metal 121 

Neutral flame 36 

Nickel, influence upon steel 91 

Open-hearth process 52 

Ores of iron 20 

^' »' '* , composition of. 21 

Oxidizing flame 36 

Permanent strain 59 

Phosphorus, influence upon steel 90 

* * , introduction of, into cast iron 28 

*' , removal of, in basic Bessemer process 47 

'< , ** <','' pu^<^ling process 40 

Phosphor-bronze 120 

Pig and ore process 52 

Pig and scrap *' 52 

Pig iron 25 

, grayer from blast-furnace using hot-blast 30 

■^ , uses of 32 

Piston-rod, material for 125 

Producer-gas, composition of. 16 

** ^' process 14 

Puddling process 35 

Rate of cooling, effect of, on distribution of carbon in cast iron 72 

Recarburization in the Bessemer process 46 






140 INDEX. 

PAGE 

Reducing flame 36 

Refining process 40 

Refractory materials 19 

Regenerative furnace, Siemens. . 16 

Remelting, effect of, upon cast iron 79 

Repeated stress, effect of no 

Resilience, elastic and ultimate 63 

Re verberatory -furnace 35 

*■* '' use in the malleable cast iron process 56 

Riveter-frame, material for 132 

Roasting 21 

Rocker-arms, material for 130 

Roughing-train 39 

Safety, factors of. 1 13 

Scrap, burnt ... 80 

Set 59 

Shaft, material for 128 

Shrinkage, fluid 82 

'* of castings * 76-82 

"■ solid 82 

Siemens-Martin, process » 52 

Siemens process $2 

' ' regenerative process * 16 

Silica in basic Bessemer process 47 

Silicon, effect on cast iron 74 

" in basic Bessemer process 4^ 

'' , influence upon steel 89 

** , introduction of, into cast iron . . . . - 27 

' < , removal of, in Bessemer process 45 

'^ , ** <* , 'Spuddling '' 38 

Slag 23 

Sources of iron 20 

Spathic ore 20 

Special steels 92-93 

Speed, cutting, of tools 92 

Spiegeleisen 4^ 

Spindles, material for 13^ 

Springs, . '< ''. I33 



INDEX. 141 

PAGE 

Spur-gears, material for 132 

Squeezer ....... ^ ... 39 

Steel castings ^ . i 56 

Steel, effect of mechanical working upon loi 

' ' , hardening of 103 

' * , tempering of ..*... 103 

Stiffness 62 

Strain 58 

" , elastic 59 

* ' , permanent 59 

Strength, ultimate 59 

' • , breaking 59 

Stress 58 

" , internal, effect of, upon stress-strain diagram 86 

Stresses, internal, in forged materials 93 

Stress, maximum 59 

Stress-strain diagram. 60, 61, 63 

Sulphur, influence upon steel 90 

*' , introduction of, into cast iron 28 

'< , removal of, in puddling process 40 

Tap-cinder 37 

Taylor- White special steel 92 

Temperature, control of, in Bessemer converter 49 

^< in acid Bessemer process 45 

<* ''basic '' '' 48 

Tempering of steel 103 

Testing materials 58 

Tool-steel process 41 

Tools, cutting speed of „ 92 

Toughening process for steel ICXD 

Tungsten, influence of, upon steel 91 

Ultimate strength 59 

Valves for engines, material for. , 130 

Water-gas, composition of 14 

'' '* process 13 



142 INDEX. 

PAGE 

Water-gas reactions 13 

Wearing surfaces, material for 122 

Wet puddling 38 

Wohler's law no 

Wood 10 

Wrought iron, composition of. 67 



( 



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Webb's Railroad Construction 8vo, 4 00 

Wellington's Economic Theory of the Location of Railways. . 

Small 8vo, 5 00 



DRAWING. 

Barr's Kinematics of Machinery 8vo, 2 50 

♦ Bartlett's Mechanical Drawing 8vo, 3 00 

Durley's Elementary Text-book of the Kinematics of Machines. 

(In preparation.) 

Hill's Text-book on Shades and Shadows, and Perspective. . 8vo, 2 00 
Jonee's Machine Design: 

Part I. — Kinematics of Machinery 8vo, 1 50 

Part XL— Form, Strength and Proportions of Parts 8vo, 3 00 

MacCord's Elements of Descriptive Geometry 8vo, 3 00 

" Kinematics; or, Practical Mechanism 8vo, 5 00 

" Mechanical Drawing 4to, 4 00 

" Velocity Diagrams 8vo, 1 50 

•Mahan's Descriptive Geometry and Stone-cutting 8vo, 1 50 

Mahan's Industrial Drawing. (Thompson.) 8vo, 3 50 

Reed's Topographical Drawing and Sketching 4to, 5 00 

Reid's Course in Mechanical Drawing 8vo, 2 00 

" Text-book of Mechanical Drawing and Elementary Ma- 
chine Design 8vo, 3 00 

Robinson's Principles of Mechanism 8vo, 3 00 

8 



Smith's Manual of Topographical Drawing. (McMillan.) Svo, 2 50 
Warren's Elements of Plane and Solid Free-hand Geometrical 

Drawing 12mo, 1 00 

" Drafting Instruments and Operations 12mo, 1 25 

" Manual of Elementary Projection Drawing 12mo, 1 50 

" Manual of Elementary Problems in the Linear Per- 
spective of Form and Shadow 12mo, 1 00 

" Plane Problems in Elementary Geometry 12mo, 1 25 

" Primary Geometry 12mo, 75 

" Elements of Descriptive Geometry, Shadows, and Per- 
spective 8vo, 3 50 

" General Problems of Shades and Shadows 8vo, 3 00 

" Elements of Machine Construction and Drawing. .8vo, 7 50 
" Problems, Theorems, and Examples in Descriptive 

Geometry Svo, 2 50 

Weisbach's Kinematics and the Power of Transmission. (Herr- 
mann and Klein.) Svo, 5 00 

Whelpley's Practical Instruction in the Art of Letter En- 
graving 12mo, 2 00 

Wilson's Topographic Surveying Svo, 3 50 

Wilson's Free-hand Perspective Svo, 2 50 

Woolf's Elementary Course in Descriptive Geometry. .Large Svo, 3 00 



ELECTRICITY AND PHYSICS. 

Anthony and Brackett's Text-book of Physics. (Magie.) 

Small Svo, 3 00 
Anthony's Lecture-notes on the Theory of Electrical Measur- 

ments 12mo, 1 00 

Benjamin's History of Electricity Svo, 3 00 

Benjamin's Voltaic Cell Svo, 3 00 

Classen's Qantitative Chemical Analysis by Electrolysis. Her- 

rick and Boltwood.) Svo, 3 00 

Crehore and Squier's Polarizing Photo-chronograph Svo, 3 00 

Dawson's Electric Railways and Tramways.. Small 4to, half mor., 12 50 
Dawson's "Engineering" and Electric Traction Pocket-book. 

16mo, morocco, 4 00 

Flather's Dynamometers, and the Measurement of Power. . 12mo, 3 00 

Gilbert's De Magnete. (Mottelay.) Svo, 2 50 

Holman's Precision of Measurements Svo, 2 00 

" Telescopic Mirror-scale Method, Adjustments, and 

Tests Large Svo, 75 

Landauer's Spectrum Analysis. (Tingle.) Svo, 3 00 

Le Chatelier's High-temperature Measurements. (Boudouard — 

Burgess.) 12mo, 3 00 

LSVs Electrolysis and Electrosynthesis of Organic Compounds. 

(Lorenz.) 12mo, 1 00 

Lyons's Treatise on Electromagnetic Phenomena Svo, 6 00 

*Michie. Elements of Wave Motion Relating to Sound and 

Light Svo, 4 00 

Niaudet's Elementary Treatise on Electric Batteries (Fish- 
back.) 12mo, 2 50 

• Parshall and Hobart's Electric Generators.. Small 4to, half mor., 10 00 
Ryan, Norris, and Hoxie's Electrical Machinery. {In preparation.) 
Thurston's Stationary Steam-engines Svo, 2 50 

• Tillman. Elementary Lessons in Heat Svo, 1 50 

Tory and Pitcher. Manual of Laboratory Physics. .Small Svo, 2 00 

9 



LAW. 

* Davis. Elements of Law 8vo, 2 50 

* " Treatise on the Military Law of United States. .8vo, 7 00 

* Sheep, 7 60 

Manual for Courts-martial 16mo, morocco, 1 50 

Wait's Engineering and Architectural Jurisprudence 8vo, 6 00 

Sheep, 6 60 
" Law of Operations Preliminary to Construction in En- 
gineering and Architecture 8vo, 5 00 

Sheep, 6 50 

" Law of Contracts 8vo, 3 00 

Winthrop's Abridgment of Military Law 12mo, 2 50 



MANUFACTURES. 

Beaumont's Woollen and Worsted Cloth Manufacture 12mo, 1 50 

Bernadou's Smokeless Powder — Nitro-cellulose and Theory of 

the Cellulose Molecule l2mo, 2 50 

Bolland's Iron Founder 12mo, cloth, 2 50 

" " The Iron Founder " Supplement 12mo, 2 50 

" Encyclopedia of Founding and Dictionary of Foundry 

Terms Used in the Practice of Moulding. . . . 12mo, 3 00 

Eissler's Modem Hi^h. Explosives 8vo, 4 00 

Eflfront's En2ymes and their Applications. (Prescott.).. .8vo, 3 00 

Fitzgerald's Bost^ i Machinist 18mo, 1 00 

Ford's Boiler Making for Boiler Makers 18mo, 1 00 

Hopkins's Oil-chemists' Handbook 8vo, 3 00 

Keep's Cast Iron 8vo 2 50 

Leach's The Inspection and Analysis of Food with Special 
Reference to State Control. {In preparation.) 

Metcalf's Steel. A Manual for Steel-users 12mo, 2 00 

Metcalfs Cost of Manufactures — And the Administration of 

Workshops, Public and Private 8vo, 5 00 

Meyer's Modern Locomotive Construction 4to, 10 00 

* Reisig's Guide to Piece-dyeing 8vo, 25 00 

Smith's Press- working of Metals 8vo, 3 00 

" Wire: Its Use and Manufacture Small 4to, 3 00 

Spalding's Hydraulic Cement 12mo, 2 00 

Spencer's Handbook for Chemists of Beet-sugar Houses. 

16mo, morocco, 3 00 
" Handbook for Sugar Manufacturers and their Chem- 
ists 16mo, morocco, 2 00 

Thurston's Manual of Steam-boilers, their Designs, Construc- 
tion and Operation 8vo, 5 00 

Walke's Lectures on Explosives 8vo, 4 00 

West's American Foundry Practice 12mo, 2 60 

" Moulder's Text-book 12mo, 2 60 

Wiechmann's Sugar Analysis Small 8vo, 2 50 

Wolff's Windmill as a Prime Mover 8vo, 3 00 

Woodbury's Fire Protection of Mills 8vo, 2 60 



MATHEMATICS. 

Baker's Elliptic Functions 8vo, 1 60 

♦ Bass's Elements of Differential Calculus 12mo, 4 00 

Briggs's Elements of Plane Analytic Geometry 12mo, 1 00 

10 



Chapman's Elementary Course in Theory of Equations. . .12mo, 

Compton'g Manual of Logarithmic Computations 12mo, 

Davis's Introduction to the Logic of Algebra 8vo, 

De Laplace's Philosophical Essay on Probabilities. (Truscott 
and Emory.) {In preparation.) 

•Dickson's College Algebra Large 12mo, 

Halsted's Elements of Geometry 8vo, 

" Elementary Synthetic Geometry 8vo, 

* Johnson's Three-place Logarithmic Tables : Vest-pocket size, 

pap., 
100 copies for 

* Mounted on heavy cardboard, 8 X 10 inches, 

10 copies for 
" Elementary Treatise on the Integral Calculus. 

Small 8vo, 

" Curve Tracing in Cartesian Co-ordinates 12mo, 

" Treatise on Ordinary and Partial Differential 

Equations Small 8vo, 

" Theory of Errors and the Method of Least 
Squares 12mo, 

* " Theoretical Mechanics ^ . . 12mo, 

•Ludlow and Bass. Elements of Trigonometry and Logarith- 
mic and Other Tables 8vo, 

" Trigonometry. Tables published separately. .Each, 

Merriman and Woodward. Higher Mathematics 8vo, 

Merriman's Method of Least Squares 8vo, 

Rice and Johnson's Elementary Treatise on the Differential 

Calculus Small 8vo, 

" Differential and Integral Calculus. 2 vols. 

in one Small 8vo, 

Wood's Elements of Co-ordinate Geometry 8vo, 

" Trigometry: Analytical, Plane, and Spherical. .. .12mo, 



MECHANICAL ENGINEERING. 

MATERIALS OF ENGINEERING, STEAM ENGINES 
AND BOILERS. 

Baldwin's Steam Heating for Buildings 12mo, 2 60 

Barr's Kinematics of Machinery 8vo, 2 50 

* Bartlett's Mechanical Drawing 8vo, 3 00 

Benjamin's Wrinkles and Recipes 12mo, 2 00 

Carpenter's Experimental Engineering 8vo, 6 00 

" Heating and Ventilating Buildings .-8vo, 3 00 

Clerk's Gas and Oil Engine Small 8vo, 4 00 

Cromwell's Treatise on Toothed Gearing 12mo, 1 50 

Treatise on Belts and Pulleys 12rao, 1 50 

Durley's Elementary Text-book of the Kinematics of Machines. 

{In preparation.) 

Flather's Dynamometers, and the Measurement of Power . . 12rao, 3 00 

Rope Driving 12mo, 2 00 

Gill's Gas an Fuel Analysis for Engineers 12mo, 1 25 

Hall's Car Lubrication 12mo, 1 00 

Jones's Machine Design: 

Part I. — Kinematics of Machinery 8vo, 1 50 

Part 11. — Form, Strength and Proportions of Parts 8vo, 3 00 

Kent's Mechanical Engineers' Pocket-book 16mo, morocco, 5 00 

Kerr's Power and Power Transmission 8vo, 2 00 

11 



1 50 

1 iO 
1 50 


1 50 
1 76 
1 50 


15 
6 00 

25 
2 00 


1 50 
1 00 


3 50 


1 50 
3 00 


3 00 
2 00 
5 00 
2 00 


3 00 


2 50 
2 00 
1 00 



MacCord's Kinematics; or. Practical Mechanism 8vo, 6 00 

** Mechanical Drawing 4to, 4 00 

" Velocity Diagrams 8vo, 1 50 

Mahan's Industrial Drawing. (Thompson.) 8vo, 3 50 

Poole's Calorific Power of Fuels Svo, 3 00 

Reid'g Course in Mechanical Drawing Svo, 2 00 

" Text-book of Mechanical Drawing and Elementary- 
Machine Design Svo, 3 00 

Richards's Compressed Air 12mo, 1 50 

Robinson's Principles of Mechanism Svo, 3 00 

Smith's Press- working of Metals Svo, 3 00 

Thurston's Treatise on Friction and Lost Work in Machin- 
ery and Mill Work Svo, 3 00 

" Animal as a Machine and Prime Motor and the 

Laws of Energetics 12mo, 1 00 

Warren's Elements of Machine Construction and Drawing. .Svo, 7 50 
Weisbach's Kinematics and the Power of Transmission. (Herr- 
mann—Klein.) Svo, 5 00 

" Machinery of Transmission and Governors. (Herr- 
mann—Klein.) Svo, 5 00 

" Hydraulics and Hydraulic Motors. (Du Bois.) .Svo, 5 00 

Wolff's Windmill as a Prime Mover Svo, 3 00 

Wood's Turbines. Svo, 2 50 

MATERIALS OF ENGINEERING. 

Bovey's Strength of Materials and Theory of Structures . . Svo, 7 50 
Burr's Elasticity and Resistance of the Materials of Engineer- 
ing Svo, 5 00 

Church's Mechanics of Engineering Svo, 6 00 

Johnson's Materials of Construction Large Svo, 6 00 

Keep's Cast Iron Svo, 2 50 

Lanza's Applied Mechanics Svo, 7 50 

Martens's Handbook on Testing Materials. (Henning.) Svo, 7 50 

Merriman's Text-book on the Mechanics of Materials Svo, 4 00 

" Strength of Materials 12mo, 1 00 

Metcalf's Steel. A Manual for Steel-users. 12mo, 2 00 

Smith's Wire: Its Use and Manufacture Small 4to, 3 00 

Thurston's Materials of Engineering 3 vols., Svo, 8 00 

Part II.— Iron and Steel Svo, 3 50 

Part III. — ^A Treatise on Brasses, Bronzes and Other Alloys 

and their Constituents Svo, 2 50 

Thurston's Text-book of the Materials of Construction Svo, 5 00 

Wood's Treatise on the Resistance of Materials and an Ap- 
pendix on the Preservation of Timber Svo, 2 00 

" Elements of Analytical Mechanics Svo, 3 00 

STEAM ENGINES AND BOILERS. 

Carnot's Reflections on tlie Motive Power of Heat. (Thurston.) 

12mo, 1 50 
Dawson's " Engineering " and Electric Traction Pocket-book. 

16mo, morocco, 4 00 

Ford's Boiler Making for Boiler ^Makers ISmo. 1 00 

Goss's Locomotive Sparks Svo, 2 00 

Hemenway's Indicator Practice and Steam-engine Economy. 

12mo, 2 00 

Button's Mechanical Engineering of Power Plants Svo, 5 00 

" Heat and Heat-engines Svo, 5 00 

13 



Kent's Steam-boiler Economy 8vo, 4 00 

Kneass's Practice and Theory of the Injector 8vo, 1 50 

MacCord's Slide-valves 8vo, 2 00 

Meyer's Modern Locomotive Construction 4to, 10 00 

Peabody's Manual of the Steam-engine Indicator 12mo, 1 50 

" Tables of the Properties of Saturated Steam and 

Other Vapors Svo, 1 00 

" Thermodynamics of the Steam-engine and Other 

Heat-engines Svo, 5 00 

" Valve-gears for Steam-engines Svo, 2 50 

Peabody and Miller. Steam-boilers Svo, 4 00 

Pray's Twenty Years with the Indicator .Large Svo, 2 50 

Pupin*s Thermodynamics of Reversible Cycles in Gases and 

Saturated Vapors. (Osterberg.) 12mo, 1 25 

Reagan's Locomotive Mechanism and Engineering 12mo, 2 00 

Rontgen's Principles of Thermodynamics. (Du Bois.) Svo, 5 00 

Sinclair's Locomotive Engine Running and Management. .12mo, 2 00 

Smart's Handbook of Engineering Laboratory Practice. .12mo, 2 50 

Snow's Steam-boiler Practice Svo, 3 00 

Spangler's Valve-gears Svo, 2 50 

" Notes on Thermodynamics 12mo, 1 00 

Thurston's Handy Tables Svo, 1 50 

" Manual of the Steam-engine 2 vols., Svo, 10 00 

Part I. — History, Structure, and Theory Svo, 6 00 

Part II. — Design, Construction, and Operation Svo, 6 00 

Thurston's Handbook of Engine and Boiler Trials, and the Use 

of the Indicator and the Prony Brake Svo, 5 00 

" Stationary Steam-engines Svo, 2 50 

" Steam-boiler Explosions in Theory and in Prac- 
tice 12mo, 1 50 

" Manual of Steam-boilers, Their Designs, Construc- 
tion, and Operation Svo, 5 00 

Weisbach's Heat, Steam, and Steam-engines. (Du Bois.).. Svo, 5 00 

Whitham's Steam-engine Design Svo, 5 00 

Wilson's Treatise on Steam-boilers. (Flather.) 16mo, 2 50 

Wood's Thermodynamics, Heat Motors, and Refrigerating 

Machines Svo, 4 00 



MECHANICS AND MACHINERY. 

Barr's Kinematics of Machinery Svo, 2 50 

Bovey's Strength of Materials and Theory of Structures. .Svo, 7 50 

Chordal.— Extracts from Letters \ 12mo, 2 00 

Church's Mechanios of Engineering Svo, 6 00 

" Notes and Examples in Mechanics Svo, 2 00 

Compton's First Lessons in Metal-working 12mo, 1 50 

Compton and De Groodt. The ^pred Lathe 12mo, 1 50 

Cromwell's Treatise on Toothed Gearing 12mo, 1 50 

" Treatise on Belts and Pulleys 12mo, 1 50 

Dana's Text-book of Elementary Mechanics for the Use of 

Colleges and Schools 12mo, 1 50 

Dingey's Machinery Pattern Making 12mo, 2 00 

Dredge's Record of the Transportation Exhibits Building of the 

World's Columbian Exposition of 1S93 4to, half mor., 6 00 

Du Bois's Elementary Principles of Mechanics: 

Vol. I. — Kinematics Svo, 3 50 

Vol. IL— Statics Svo, 4 00 

Vol. III.— Kinetics Svo, 3 50 

13 



Du Bois's Mechanics of Engineering. Vol. 1 Small 4to, 7 50 

Vol.11 Small 4to, 10 00 

Durley'g Elementary Text-book of the Kinematics of Machines. 

{In preparation.) 

Fitzgerald's Boston Machinist 16mo, 1 00 

Mather's Dynamometers, and the Measurement of Power. 12mo, 3 00 

" Rope Driving 12mo, 2 00 

Ooss's Locomotive Sparks .8vo, 2 00 

Hall's Car Lubrication 12mo, 1 00 

Holly's Art of Saw Filing 18mo, 75 

* Johnson's Theoretical Mechanics 12mo, 3 00 

Johnson's Short Course in Statics by Graphic and Algebraic 

Methods. {In preparation.) 
Jones's Machine Design: 

Part I. — Kinematics of Machinery 8vo, 1 50 

Part 11. — Form, Strength and Proportions of Parts. .. .8vo, 3 00 

Kerr's Power and Power Transmission 8vo, 2 00 

Lanza's Applied Mechanics 8vo, 7 60 

MacCord's Kinematics; or, Practical Mechanism 8vo, 5 00 

" Velocity Diagrams 8vo, 1 50 

Merriman's Text-book on the Mechanics of Materials 8vo, 4 00 

* Miehie's Elements of Analytical Mechanics 8vo, 4 00 

Reagan's Locomotive Mechanism and Engineering 12mo, 2 00 

Reid's Course in Mechanical Drawing 8vo, 2 00 

" Text-book of Mechanical Drawing and Elementary 

Machine Design 8vo, 3 00 

Richards's Compressed Air 12mo, 1 50 

Robinson's Principles of Mechanism 8vo, 3 00 

Ryan, Norris, and Hoxie's Electrical Machinery. {In preparation.) 

Sinclair's Locomotive-engine Running and Management. .12mo, 2 00 

Smith's Press-working of Metals Svo, 3 09 

Thurston's Treatise on Friction and Lost Work in Machin- 
ery and Mill Work 8vo, 3 00 

" Animal as a Machine and Prime Motor, and the 

Laws of Energetics 12mo, 1 00 

Warren's Elements of Machine Construction and Drawing. .8vo, 7 50 
Weisbach's Kinematics and the Power of Transmission. 

(Herrman — Klein.) Svo, 5 00 

" Machinery of Transmission and Governors. (Herr- 

(man — Klein.) 8vo, 5 00 

Wood's Elements of Analytical Mechanics 8vo, 3 00 

" Principles of Elementary Mechanics 12mo, 1 25 

" Turbines 8vo, 2 50 

The World's Columbian Exposition of 1893. 4to, 1 00 

METALLURGY. 

Egleston's Metallurgy of Silver, Gold, and Mercury: 

Vol. I.-Silver Svo, 7 50 

Vol. n.— Gold and Mercury 8vo, 7 60 

Keep's Cast Iron 8vo, 2 50 

Kunhardt's Practice of Ore Dressing in Lurope 8vo, 1 50 

Le Chatelier's High-temperature Measurements. (Boudouard — 

Burgess.) 12mo, 3 00 

Metcalf's Steel. A Manual for Steel-users 12mo, 2 00 

Thurston's Materials of Engineering. In Three Parts 8vo, 8 00 

Part II.— Iron and Steel 8vo, 3 50 

Part m. — A Treatise on Brasses, Bronzes and Other Alloys 

and Their Constituents Svo, 2 50 

14 



MINERALOGY. 

Barringer's Description of Minerals of Commercial Value. 

Oblong, morocco, 2 50 

Boyd's Resources of Southwest Virginia 8vo, 3 00 

" Map of Southwest Virginia Pocket-book form, 2 00 

Brush's Manual of Determinative Mineralogy. (Penfield.) .8vo, 4 00 

Chester's Catalogue of Minerals 8vo, paper, 1 00 

Cloth, 1 25 

" Dictionary of the Names of Minerals Svo, 3 50 

Dana's System of Mineralogy Large Svo, half leather, 12 50 

" First Appendix to Dana's New " System of Mineralogy." 

Large 8vo, 1 OU 

" Text-book of Mineralogy Svo, 4 00 

" Minerals and How to Study Them 12mo, 1 59 

" Catalogue of American Localities of Minerals . Large 8vo, 1 00 

** Manual of Mineralogy and Petrography 12mo, 2 00 

Eglestom's Catalogue of Minerals and Synonyms 8vo, 2 50 

Hussak's The Determination of Rock-forming Minerals. 

(Smith.) Small 8vo, 2 00 

• Penfield's Notes on Determinative Mineralogy and Record of 

Mineral Tests Svo, paper, 50 

Rosenbusch's Microscopical Physiography of the Rock-making 

Minerals. (Idding's.) Svo, 5 00 

♦Tillman's Text-book of Important Minerals and Rocks.. Svo, 2 00 

Williams's Manual of Lithology Svo, 3 00 



MINING. 

Beard's Ventilation of Mines 12mo, 2 50 

Boyd's Resources of Southwest Virginia Svo, 3 00 

" Map of Southwest Virginia. Pocket-book form, 2 00 

♦Drinker's Tunneling, Explosive Compounds, and Rock 

Drills 4to, half morocco, 25 00 

Eissler's Modern High Explosives Svo, 4 00 

Goodyear's Coal-mines of the Western Coast of the United 

States 12mo, 2 50 

Ihlseng's Manual of Mining Svo, 4 00 

Kunhardt's Practice of Ore Dressing in Europe Svo, 1 50 

O'Driscoll's Notes on the Treatment of Gold Ores Svo, 2 00 

Sawyer's Accidents in Mines Svo, 7 00 

Walke's Lectures on Explosives Svo, 4 00 

Wilson's Cyanide Processes 12mo, 1 50 

Wilson's Chlorination Process 12mo, 1 50 

Wilson's Hydraulic and Placer Mining 12mo, 2 06 

Wilson's Treatise on Practical and Theoretical Mine Ventila- 
tion 12mo, 1 26 



SANITARY SCIENCE. 

Folwell's Sewerage. (Designing, Construction and Maintenance.) 

Svo, 3 00 

" Water-supply Engineering Svo, 4 00 

Fnertes's Water and Public Health 12mo, 1 50 

" Water-filtration Works 12mo, 2 50 

15 



Gerhard's Guide to Sanitary House-inspection 16mo, 1 00 

Goodrich's Economical Disposal of Towns' Ref use ... Demy 8vo, 3 50 

Hazen's Filtration of Public Water-supplies 8vo, 3 00 

Kiersted's Sewage Disposal 12mo, 1 25 

Leach's The Inspection and Analysis of Food with Special 

Reference to State Control. {In preparation.) 
Mason's Water-supply. (Considered Principally from a San- 
itary Standpoint. 3d Edition, Rewritten 8vo, 4 GO 

" Examination of Water. (Chemical and Bacterio- 
logical.) 12mo, 1 25 

Merriman's Elements of Sanitary Engineering 8vo, 2 00 

Nichols's Water-supply. (Considered Mainly from a Chemical 

and Sanitary Standpoint.) (1883.) 8vo, 2 50 

Ogden's Sewer Design 12mo, 2 00 

• Price's Handbook on Sanitation 12mo, 1 50 

Richards's Cost of Food. A Study in Dietaries 12mo, 1 00 

Richards and Woodman's Air, Water, and Food from a Sani- 
tary Standpoint 8vo, 2 00 

Richards's Cost of Living as Modified by Sanitary Science . 12mo, 1 00 

* Richards and Williams's The Dietary Computer 8vo, 1 50 

Rideal's Sewage and Bacterial Purification of Sewage 8vo, 3 60 

Turneaure and Russell's Public Water-supplies 8vo, 5 00 

Whipple's Microscopy of Drinking-water 8vo, 3 50 

Woodhull's Notes on Military Hygiene 16mo, 1 50 



MISCELLANEOUS. 

Barker's Deep-sea Soundings 8vo, 2 00 

Emmons's Geological Guide-book of the Rocky Mountain Ex- 
cursion of the International Congress of Geologists. 

Large 8vo, 1 50 

Ferrel's Popular Treatise on the Winds 8vo, 4 00 

Haines's American Railway Management 12mo, 2 50 

Mott's Composition, Digestibility, and Nutritive Value of Food. 

Mounted chart, 1 25 

" Fallacy of the Present Theory of Sound 16mo, 1 00 

Ricketts's History of Rensselaer Polytechnic Institute, 1824- 

1894 Small 8vo, 3 00 

Rotherham's Emphasised New Testament Large 8vo, 2 00 

" Critical Emphasised New Testament 12mo, 1 50 

Steel's Treatise on the Diseases of the Dog 8vo, 3 50 

Totten's Important Question in Metrology 8vo, 2 50 

The World's Columbian Exposition of 1893 .4to, 1 00 

Worcester and Atkinson. Small Hospitals, Establishment and 
Maintenance, and Suggestions for Hospital Architecture, 

with Plans for a Small Hospital 12mo, 1 25 



HEBREW AND CHALDEE TEXT-BOOKS. 

Green's Grammar of the Hebrew Language 8vo, 3 00 

" Elementary Hebrew Grammar 12mo, 1 25 

" Hebrew Chrestomathy 8vo, 2 00 

Gesenius's Hebrew and Chaldee Lexicon to the Old Testament 

Scriptures. (Tregelles.) Small 4to, half morocco, 5 00 

Letteris's Hebrew Bible 8vo, 2 25 

16 



AUG 21 1902 

1 COPY DEI. TOCAT niV. 
AUG. n 1902 

AUG. 2G 190? 



